Ectodermal Invagination Research Articles

Congenital Fistula of Lacrimal Duct

CONGENITAL fistula of the lacrimal duct is very rare, and is usually associated with other congenital anomalies (Duke-Elder, 1932, 1952; Gray, 1949; Spaeth, 1948). The epithelium of the ducts and alveoli of the lacrimal gland is derived from a series of ectodermal invaginations in the region of the superior conjunctival fornix. Early buds form the orbital portion, while secondary buds from above appear later and form the palpebral lobe at the 40-60 mm. stage of the foetus. The stalk of the ectodermal invaginations, at first solid, are later canalized (50-55 mm.). The full development of the gland occurs at about 3 to 4 yrs. The gland ducts are about twelve in number, two to five being derived from the orbital lobe, and six to eight from the palpebral lobe; they all pass through the palpebral lobe as would be expected from their development. The majority of ducts open into the lateral part of the superior fornix, but a large duct (which may be called the inferolateral duct) traverses the extreme outer end of the gland, passes just deep to the conjunctival epithelium, and opens a few millimetres lateral to and some distance below the external commissure. The case described below is that of a little girl who had a congenital fistula of the right inferolateral lacrimal duct and right dacryocystitis with no associated deformity of the external canthus or elsewhere.

The Hair of California Mammals with Keys to the Dorsal Guard Hairs of California Mammals

It has long been recognized that hairs are as characteristic of mammals as are the glands which give the class its name. When hairs do not appear in the adult animal, as in Odontoceti, they are at least present in the embryo. They may be confined, as in Mysticeti, to the region of the nares, or they may appear over the entire body, as in the Reindeer, in which even the usually bare mammalian snout is hairy. In recognition of this characteristic presence of hair it was at one time proposed that the class should be named Trichozoa or Pilifera. In recent years significant investigations on hair have been few, the latest contribution of note being that of Hamilton et al. (1951). In the latter part of the nineteenth century and early part of the twentieth century more extensive research was accomplished. However, merely 47 of the more than 3000 references in the possession of the author deal primarily with hair as a means of classification or identification, and the majority of these are anthropological studies on human hair. Only 17 concern themselves wholly or in sizeable part with the problem of hair of mammals other than man. With respect, then, to its systematic usefulness little research on hair has been done, and the taxonomic value of hair is a subject on which all authors have not agreed. Cole (1924: 120) and Nason (1948: 358), studying bats, both came to the conclusion that hair is of little use- in identification. Mathiak (1938), Williams (1938), and Brown (1942) all arrived at the opposite conclusion, and prepared aids for identifying certain mammals on the basis of hair alone. With this latter group the present author is in complete agreement. The ability to make positive identification of mammalian hair is of great value in fields such as criminology and paleontology and particularly in the field of food habits studies. Fortunately hair is a relatively durable feature, and a high percentage of the shafts recovered from the digestive tracts of birds and mammals are capable of being used for the purpose of making identification. HAIR STRUCTURE The hair shaft is a highly keratinized column lacking both nerves and blood vessels. The follicle is formed embryologically as an ectodermal invagination of cells from the malpighian layer of the epidermis. This invagination splits, and cells proliferating from the ectodermal base of the follicle, and nourished by a deeper-lying dermal papilla, move peripherally as the hair shaft proper (Danforth, 1925: 23). As the hairs move outward from the basal.bulb, the cells become more highly keratinized and tend to lose their individual identity. 480

The reproductive system and embryology of the snail Pomatias elegans (Müller)*

SUMMARY.A description is given of the anatomy and histology of the genital system of the terrestrial prosobranch Pomatias elegans, of the structure of its egg capsule and of the development of the embryo until the time of hatching. Reproduction and development are compared with those processes in marine forms.The breeding season is prolonged, extending from February until August, and, correlated with this, there is little seasonal variation in the size of the genital system.The male is more specialized than in the related Littorina spp. because the pallial and penial ducts are completely closed, but in the female specialization has led to a secondary opening of the pallial duct to assist the expulsion of the large egg capsule. This has necessitated changes of structure in the organ concerned with copulation and the storage of sperm. The sac homologous with the receptaculum in other species has developed a direct opening into the mantle cavity and acts as a posteriorly situated bursa copulatrix and the gonadial duct is comparatively wide and functions as the receptaculum seminis. There is no gonopericardial duct.The extremely glandular pallial oviduct secretes a capsule 2 mm. in diameter around the single small egg (0±13 mm. diameter) and it is the albumen and the gelatinous capsule wall that are used for food during the three months of intra‐capsular development and not a large accumulation of yolk. Absorption of water and salts from the surrounding soil also occurs and there is some factor present in natural soil water which is necessary for development. Correlated with the lack of yolk, invagination and epiboly are of equal importance in gastrulation. Early in this process the mesoderm mother cell, 4D, moves between the ectoderm and endoderm.Intra‐capsular development continues until the animal is a miniature adult, and the trochophore and veliger stages are considerably modified. No spacial larval sensory, excretory or respiratory organs are formed, but a large embryonic structure, the cephalic mass, develops in the velar region. This has an absorptive function. The cephalic mass begins to differentiate during the early veliger stage, and is most fully developed during the mid and late veliger stages; it is steadily reduced and has disappeared completely by the time of hatching. As the cephalic mass becomes smaller relative to the size of the animal, the digestive gland, which develops precociously, becomes larger.Development of the principal organs is as in prosobranchs like Haliotis and Patella. The mantle cavity develops in the early and mid veliger stages partly from the pretorsional right member of a pair of ectodermal invaginations which are formed in the postero‐ventral part of the visceral mass, one on each side of the rectum, and partly as a result of the growth of the mantle skirt. The kidney and pericardium develop from adjacent mesodermal rudiments on the pretorsional right side of the embryo and the fact that these structures were originally paired is shown by the presence of a vestige on the left. The principal ganglia of the nervous system are all formed separately by delamination from the ectoderm.The widest departure from the course of development described in other prosobranchs is found in the process of torsion. It is the result of differential growth alone and at the time it occurs, no muscles capable of contraction are differentiated.

Sacrococcygeal pilonidal cyst

1. 1. “Hair-nest” sinus occurring at the base of the spine is more properly designated sacrococcygeal pilonidal sinus. 2. 2. The first reference in the literature to the condition is a letter by Dr. A. W. Anderson, Gray, Maine, written to the Editor of The Boston Medical and Surgical Journal on February 8, 1847. 3. 3. The term “pilo-nidal sinus” was used for the first time by Dr. R. M. Hodges in a paper read before the Boston Society for Medical Improvement on November 8, 1880. 4. 4. The theory of nerve origin is based on the assumption that remnants of the embryonic neural canal persist as epithelial rests. 5. 5. The theory of ectodermal invagination predicates a special downgrowth of epithelium from the true skin as in the formation of the breast and external ear. 6. 6. The theory of vestigial sex-gland origin assumes the presence of a vestigial secondary sex gland in the sacrococcygeal region which becomes active at adolescence. 7. 7. Sacrococcygeal pilonidal cyst disease is found primarily in hairy, obese, white, male adults twenty to thirty years of age. The predominant complaints are pain and drainage in the coccygeal region. 8. 8. Diagnostic signs are abscess formation and one or more midline sinus openings over the sacrococcygeal joint. 9. 9. Various methods of treatment are discussed. Best results have been obtained by excision and open packing.

INTRACRANIAL EPIDERMOIDS OCCURRING SIMULTANEOUSLY BELOW AND ABOVE THE TENTORIUM

The term epidermoid (cholesteatoma) refers to a slow growing, cystic neoplasm which may occur in or beneath the scalp, within or about the orbit, in the neck, jaws, middle ear, mastoid, cranial bones or elsewhere along the craniospinal axis. The manner of origin is said to be by inclusion of epiblastic tissue during the closure of clefts or at a point of contact of ectodermal invagination with other tissues in the development of the embryo. 1 Another presumptive source is epidermal implantation resulting from trauma, an example of which has been recorded by Graumann. 2 Up to the time of writing 205 cases of intracranial epidermoid tumor have been recorded in the literature. Of this number there were 7 in which the lesion was situated in both the supra-tentorial and the infratentorial position. The purpose of this paper is to review these 7 cases and to add the eighth. The

The Embryology and Affinities of the Symphyla, based on a Study of Hanseniella agilis

The Embryology and Affinities of the Symphyla, based on a Study of Hanseniella agilis

The Later Embryology of Rhodnius prolixus

ABSTRACT The development of the external features of the embryo from the time at which the germ-layers are laid down until hatching is described. The fate of the embryonic membrane is followed, and the formation of a ‘cuticular’ layer round the whole embryo produced by the glands which result from the modification of the first abdominal appendages (pleuropodia). The central nervous system is produced in a similar manner to that of other insects. Two parallel longitudinal rows of neuroblasts separate from the dermatoblasts and give rise to the longitudinal nerve-cords. In between them is the neural groove, and cells dorsal to the neural groove produce a median cord. Neuroblasts in the protocerebral, antennary, and pre- mandibular segments form the supra-oesophageal nerve-mass, and those in the mandibular, maxillary, and labial the sub- oesophageal mass. At first three thoracic and eight abdominal ganglia are formed. Later concentration occurs, and by 18 days all the ventral ganglia are located in the thorax, the metathoracic ganglia being particularly large. The sympathetic nervous system arises from the dorsal wall of the stomodaeum. The corpus allatum originates as a pair of ectodermal cellmasses which appear to be invaginated from the maxillary segment. The ectodermal invagination to form the tentorium, glands, and spiracular system is described. Oenocytes appear previous to the ectodermal cells producing their cuticular layer. They become more numerous and much smaller after cuticle formation. The fore- and hind-gut develop normally. The Malpighian tubules are developed from ectoderm. The mid-gut arises in three parts, and the yolk becomes restricted to the middle part in the late embryos. From the mesoderm the usual structures are derived. Musculature of limbs and body is of two distinct kinds. The heart, fat-body, and splanchnic muscles are derivatives of the mesoderm. The germ-cells are defined before the germ-band invagi- nates. Later they are to be found, round the coeloms of the posterior abdominal segments. They migrate anteriorly and form complete gonads 10 days before hatching. The structure of the head of Rhodnius supports the orthodox view that the head of insects is composed of six segments. Evidence from the development of Rhodnius suggests that the insect labrum represents a pair of appendages. Time-table of development at 21° C. and 90 per cent, relative humidity.

Morphology and development of the femoral chordotonal organs of melanoplus differentialis (orthoptera, acrididae)

AbstractChordotonal organs are present in the prothoracic, mesothoracic and metathoracic femora of Melanoplus differentialis. These have been described and their development traced from ectodermal invaginations located at the proximal and distal ends of the prothoracic and mesothoracic and at the distal end of the metathoracic femora of the embryo.

Memoirs: Observations on the Embryology of Corynodes Pusis (Coleoptera, Chrysomelidae)

An account is given of the embryology of Corynodes pusis Marsh, a Chrysomelid beetle feeding on Asclepias fruticosa. The development of this species is remarkably similar to that of Euryope terminalis, an allied species previously investigated by the writer (1931, 1932). In both species there is a very early differentiation of the germinal protoplasm at the posterior pole, and the genital rudiment makes its appearance in this position immediately the blastoderm is completed. The lower layer of cells is derived by proliferation and invagination of cells in the mid-ventral line, and this process is considered to represent the gastrulation phase of other invertebrate embryos. The cells resulting from this invagination differentiate into lateral mesoderm and median endoderm. The mesoderm gives rise to appendicular and segmental muscles, fat-body, cardioblasts, and the muscle-layer of the mesenteron. The epithelial layer of the mid-gut is considered to develop from the median endoderm, which gives no indication in either of these species of a bipolar condition. In this respect the development of these two species differs from that of other recently investigated insects, but shows some resemblance to the condition described by Leuzinger and Wiesmann (1926) in the Orthopteran, Carausius morosus. The development of the ectoderm is essentially similar to that of other insect embryos. The stomodaeum and proctodaeum are imaginations of the ectoderm, as are also the respiratory and excretory systems. In addition to the two pairs of thoracic and eight pairs of abdominal spiracles observed in Euryope, there are vestigial spiracular invaginations on the ninth and tenth abdominal segments of Corynodes. In both species the Malpighian tubules arise as three separate pairs of outgrowths of the wall of the proctodaeum, and there is no indication that any part of their wall is derived from the endoderm, an opinion recently expressed by Henson (1932) when describing the condition in the embryo of Pieris. The tentorium is rather better developed in Corynodes than in Euryope, and in the embryo four pairs of cephalic ectodermal invaginations were observed to arise in a series one behind the other on the antennary, mandibular, maxillary, and labial segments.

On the Development of the Male Genitalia and the Efferent Genital Ducts in Lepidoptera

ABSTRACT A general account of the internal reproductive organs and the external genitalia and their development is given. The ‘penis lobes’ develop earlier than the ‘valvae lobes ‘, and independently of them. The tegumen is the modified ninth tergite. The tenth segment is visibly distinguished into a tergal and sternal part in the pupal stages, and the anal tube passes between the two sclerites. The uncus and the gnathos are dorsal and ventral processes respectively of the tenth segment. The anellus lobes develop as lateral processes of the ninth sternite on either side of the penis. The vasa deferentia during larval life do not extend beyond the eighth abdominal segment and lie in a latero-ventral position. They meet the extensions from the ectodermal ‘ductus ejaculatorius duplex’ during the last larval stadium. From the earliest caterpillar stage there exists a pair of ectodermal ducts formed by the differentiation of the epidermis on the ninth sternite. Towards the end of larval life they divide by constriction to form the accessory glands and the ‘ductus ejaculatory duplex’. At this stage they extend on either side to meet the vasa deferentia. The vesiculae seminales develop by distension from the region of junction between the vasa deferentia and the proximal portion of the ejaculatory duct. The ‘ductus ejaculatorius simplex’ arises as an ectodermal invagination between the pair of ‘penis lobes ‘during the final larval instar. It is established that, with the exception of the vasa deferentia, all the remaining elements in the efferent genital system are derived from the ectoderm.

Memoirs: Studies On the Development of the Genitalia and the Genital Ducts in Insects. I. Female of Orthoptera and Dermaptera

1. The anterior ovipositor lobes (ventral valves) of Orthoptera are serially homologous with the lateral ovipositor lobes (dorsal valves) and represent gonocoxites from which no telopodites, corresponding to the inner valves, are differentiated. 2. The common oviduct originates as an unpaired ectodermal (hypodermal) invagination, in Blattella from the seventh intersternal membrane, in Locustana , Colemania, and Forficula between the seventh and eighth sterna, ending blindly, internally, between the ends of the mesodermal oviducts lying near the posterior margin of the seventh sternum. 3. In Blattella and Forficula the early condition is retained up to the adult stage; in Locustana and Colemania the common oviduct is secondarily extended posteriorly along the eighth sternum in the first instar, the gonopore coming to open in later instars, and in the adult on the inner reflexed surface of the eighth sternum. 4. Grooves are present in the early stages of Locustana, Colemania, and Blattella , between the bases of the ovipositor lobes on the eighth and ninth sterna, which become tubular anteriorly, giving rise each to an accessory genital invagination. The invagination from the eighth gives rise to the spermatheca in Locustana and Colemania; in Blattella it atrophies in late nymphal stages. The invagination from the ninth gives rise to the paired colleterial gland in Blattella; in Locustana and Colemania it develops slowly and gives rise to a vestigial accessory genital invagination. In Forficula no ovipositor lobes are present, and the invagination from the eighth arises practically intersegmentally between sterna 8 and 9. It also gives rise to the spermatheca in the adult. No accessory genital invagination is developed from the ninth sternum. 5. In Blattella four spermathecae are present. They originate as two pairs of separate hypodermal invaginations from the seventh intersternal membrane, morphologically posterior to the common oviduct invagination. 6. The primitive position of the single gonopore in the Orthoptera and Dermaptera is between sterna 7 and 8, its position in present-day Locustidae, Tettigoniidae, Gryllidae on the eighth sternum being secondary. 7. The spermathecal function was ancestrally associated with the accessory genital invagination from the eighth sternum in the Orthoptera. The four spermathecae of Blattella represent secondarily developed structures which do not correspond to the spermathecae of other Blattids, e.g. Periplaneta and other Orthoptera. 8. There is no evidence that part of the common oviduct is of mesodermal derivation or that it has a paired origin in the Orthoptera and in insects in general. 9. A hypothetical ancestral condition of the oviducal system and accessory organs is deduced for insects in general. The paired mesodermal oviducts opened separately within the seventh intersternal membrane, two gonopores being present. Accessory genital invaginations, possibly paired, were present on the eighth and ninth sterna at the bases of the gonopods, a spermathecal function probably being associated with the invagination(s) on the eighth sternum. Phylogenetic specialization consisted in an early acquisition of an ectodermal common oviduct and single gonopore between the seventh and eighth sterna, possibly polyphyletic, and a later extension posteriorly of the common oviduct and single gonopore on to the eighth and on to the ninth sterna, this posterior extension having definitely taken place polyphyletically.

Memoirs: The Morphology and Development of the Genitalia and Genital Ducts of Homoptera and Zygoptera as Shown in the Life Histories of Philaenus and Agrion

1. In the male Philaenus and Agrion the vasa deferentia terminate on the ninth segment in the early stages. An ectodermal invagination from that segment joins them subsequently and thus the male gonopore is established. 2. The accessory glands develop in Philaenus male from the anterior end of the swollen extremities of the vasa deferentia and the vesiculae seminales from a still more forward region. 3. The accessory glands of the male are mesodermal in origin and not ectodermal as some authors state. 4. There is no evidence as to the existence of a ‘pair of ectodermal ejaculatory’ ducts either in Philaenus orin Agrion, and reasons are adduced to show that they do not exist at all in the higher Insecta. 5. In the female nymph of Philaenus the oviducts terminate on the seventh segment. They are subsequently joined by an ectodermal invagination from the seventh segment. The common oviduct is formed in two parts: the anterior part is derived from the posterior region of the invagination on the seventh and the posterior region is formed as a groove from the ectodermis of the eighth segment and subsequently this groove is converted into a tube. When the second part is completed it is in connexion with the invagination from the seventh and opens to the outside on the eighth segment. The ectodermal invagination from the seventh also gives rise to the spermatheca. A median accessory gland develops as an invagination from the ninth segment between the bases of the inner ovipositor lobes. A pair of accessory glands develop as paired imaginations from the anterior region of the ninth segment. 6. In the female nymph of Agrion the oviducts fuse to form a single duct and terminate in the middle of the eighth segment. Posteriorly an ectodermal invagination from the eighth segment meets this duct and lies in a position dorsal to it. Later on the ectodermal invagination develops a spermatheca dorsally and the mesodermal and the ectodermal ducts unite into one. The accessory glands develop as paired ectodermal invaginations from the anterior region of the ninth segment. 7. The female gonopore is not homologous in the different groups of insects. The vaginal opening in Orthoptera, Hymenoptera, Homoptera, Diptera, and Lepidoptera is homologous. The vaginal opening in Coleoptera is homologous with the oviducal opening of Lepidoptera, with the opening of the accessory gland of Homoptera, Hymenoptera, Diptera, Isoptera, and the opening of the spermatheca in some Orthoptera. 8. The common oviduct, being formed differently in the different groups is not homologous. The accessory organs, e. g. spermatheca, are not homologous in the different groups. 9. There is no evidence to show that the common oviduct is of paired origin. 10. The occurrence of a median accessory structure on the ninth segment which develops in the young as an invagination between the bases of the inner ovipositor lobes is very general in the higher Insecta. In some it functions as a gland, in others as a storehouse for spermatozoa. 11. The homology of the paired accessory glands is indicated. 12. The male genital ducts are not strictly homologous with those of the female. The homologue of the ejaculatory duct is the invagination from the ninth segment in the female. 13. The Odonata stand isolated in having a mesodermal region for the common oviduct and in the peculiar development of the two processes between the anterior ovipositor lobes. 14. The probable lines of evolution of the female efferent system in Insecta are indicated. The study of the development of the female efferent system indicates that the groups Orthoptera, Homoptera, Lepidoptera, and Diptera are very closely allied. Coleoptera seem to have had quite a different line of evolution from the above groups in this respect. 15. The adult Odonatan anatomy of the genital organs in the female as observed by me is in some respects different from that described by Tillyard. In conclusion I wish to express my deep sense of gratitude towards Professor Balfour-Browne and Dr. J. W. Munroe, both of whom have always been ready to help me. My colleague Mr. R. I. Nel, who is working on similar lines in this department,, has rendered me valuable help, not only in matters connected with the subject proper but also in translating difficult German references. I am also indebted to Mr. Peter Gray who helped me a good deal in translating references in Italian.

The Atrium and the Prostate Gland in the Microdrili

ABSTRACT 1. The atrium in two species of the Naididae is described. The prostate in Nais elinguis forms the wall of the vas deferens; in Slavina punjabensis it covers the atrium. The atrium is formed as an ectodermal invagination and always occupies a position at the end of a short vas deferens. The atrial epithelium in the sexually mature Stylaria lacustris and Slavina punjabensis is replaced by the prostatic secretion which passes through it; it is not really composed of glandular cells as has been so far considered. 2. The prostate cells in the Naididae may surround the atrium or the vas deferens or both. The cells appear to penetrate into the muscle-fibres of the atrial wall in order to directly communicate with the atrial epithelium. They also become more or less completely changed in the late stage of sexual maturity into the secretion and lose their identity. The prostate cells are peritoneal in origin. The prostate may be absent or rudimentary in some species of the Naididae. 3. Various stages in the development of the sperm-duct in Tubifex barbatus are described. The atrium is shown to be a part of the vas deferens and hence mesodermal in origin. The prostate lies near the seminal funnel on the ventral side of the vas deferens just above the ovary; in the early condition it is a deeply stained mass of nuclei with a little cytoplasm and continuous with the peritoneal layer of the vas deferens in front and behind. 4. The atrium and the prostate in Tubifex tubifex and Limnodrilus udekemianus are described. The prostate is peculiar in the species of the Tubificidae investigated in the fact that the secretion of a fibrillar appearance forms the centre of the gland, while the cells occupy the periphery. The fibrillar secretion flows into the atrial epithelium, through a regular passage or opening where the muscular wall is absent. This appearance probably led previous workers to suppose that the prostate cells open by long ductules at the point of com-munication with the atrium. There is no evidence whatsoever that the prostate arises as an outgrowth from the atrial epithe-lium; on the other hand it is obviously peritoneal in origin. 5. The cytoplasm in the prostate cells is basophil as distin-guished from the acidophil central part with the secretion, and in Tubifex tubifex during the advanced condition of the gland generally contains basophilous granules, which pass with the fibrillar secretion as secretory products into the atrium. The prostate cells in the advanced sexual condition lose their structure and do not show mitochondria. 6. The atrial epithelium in all the species of the Tubificidae considered is not composed of gland-cells. It is on account of the prostatic secretion, which passes through it into the atrial lumen, that it degenerates and its cells break down. 7. The prostatic secretion in the Naididae and Tubificidae appears as a fluid of thick consistency. Its function is mainly to cement or unite sperms received in the atrium. It does not contain mucin, but in sections of Tubifex tubifex prepared according to the Mann-Kopsch method the central conducting part of the gland and a portion of the atrial wall show the presence of a large amount of fat, mainly olein, or some lipoid substance, which reduces osmium tetroxide, and thus becomes deep black like the dictyosomes of the Golgi apparatus. 8. The homologies of the atrium and the prostate are briefly discussed in the various families of the Microdrili. 9. Peculiar features in the structure of the vas deferens in Tubifex tubifex and Limnodrilus udekemianus are described.

Memoirs: The Genital Organs of Stylaria lacustris, with an account of thier Development

1. The genital organs of Stylaria lacustris are described in detail. The vas deferens opens into the atrium on the anterior face near the opening of the ejaculatory duct and not at the top as described by all the previous authors. The prostate surrounds not only the atrium but also the vas deferens in segment 6. 2. The prostate secretion passes through the atrial epithelium, which consequently hypertrophies and disappears 3. The development of the genital organs proceeds with great rapidity when the sexual phase appears, which occurs only once a, year from the end of September to the beginning of December. There is no long intervening period between the development of the gonads, and other genital organs. 4. The order of development seems to be connected with the time or order of their functioning. 5. The gonads are peritoneal in origin. The sperm-sac and orisac are large portions of the body-cavity enclosed by the extension backwards of septa ⅚ and 6/7 respectively. The yolk-mass is formed by a process of metabolic change in the cytoplasm of some of the ova. 6. The sperm-duct is partly peritoneal in origin and partly an ectodermal invagination. The funnel and the vas deferens rudiments arise by a proliferation of the peritoneal cells on the anterior face of septum ⅚, which assumes the form of a deeply shining plate of columnar cells with prominent nuclei. This after the funnel rudiment becomes the sperm-cord and penetrates the septum in front of the ovary, reaching near the body-wall the atrial rudiment, which is soon formed as an ec todermal invagination. The prostate cells arise from the peritoneum near the rentral body-wal1 of the sixth segment in the neighbourhood of the atrial rudiment. 7. The rudimentary female funnel, which opens ont at the female opening, arises as, an outgrowth from the peritoneum at the base of septum 6/7. 8. The spermatheca srises as an invagination from the ectoderm. I agree with Bergh that the sperm, zthecae are to be considered as new structures, and not phylogenetically connected with the genital ducts as Gatenby supposes to be the case in Tubifex rivulorum. 9. A fern stages obtained showing the development of these organs in Nais e1inguis confirm the above observntions.

AN EXPERIMENTAL DEMONSTRATION OF THE REGENERATION OF THE PHARYNX OF ALLOLOBOPHORA FROM ENDODERM

SEVERAL recent investigators have shown with more or less probability that the lining of the new pharynx which develops during the regeneration of the head in certain earthworms comes from the endoderm, while the pharynx of the embryo is lined by ectoderm.' It seemed that by means of experimental methods this relation might be definitely determined. In the following pages I shall describe some experiments on Allolo bophora foetida that demonstrate, I think, that the lining of the new pharynx is in fact derived from the endoderm. Hescheler showed, as the result of observations made prin cipally on Allolobophora terrestris, that when the five anterior segments are cut off the pharynx is regenerated by a growing forward of the old digestive tract up to the third segment, and that the new buccal cavity occupying the first three segments is formed by an ectodermal invagination. The old pharynx was not completely removed in these operations, since in the normal worm its cavity frequently extends beyond the fifth segment and its thickened muscular dorsal wall always goes back into the sixth, so that Hescheler's results are open to the objection that in his experiments apart, at least, of the old pliaryngeal wall always remained behind as a possible source for the regeneration of the new pharynx. Rievel in experimenting on certain Lumbricidae (Allolobo phora foetida, Allolobophora terrestris, Lumbricus rubellus) cut off anterior ends consisting of between one-third to two thirds of the entire body. He arrives at the conclusion that the pharynx is regenerated from the walls of the digestive tract