Ventral Outgrowth Research Articles

Анатомо-топографические особенности заднебедренной группы мышц тазобедренного сустава у благородного пятнистого оленя

The article presents the morphological and functional characteristics of the posterior femoral muscle group of the hip joint in the noble spotted deer. The research was carried out at the Department of Anatomy and Histology of Animals named after Professor A. F. Klimov of the Moscow State Academy of Veterinary Medicine and Biotechnology – MBA named after K. I. Scriabin. The objects of research were a mature noble spotted deer (n=5). The article presents anatomical features of the posterior femoral group of hip extensors in the subspecies of red deer – spotted deer, which are absent in the available literature. The topological features of anatomical formations of the sciatic tubercle are revealed – the presence of dorsal, lateral and medial outgrowths on it. The last outgrowth of the spotted deer is on the same level with the lateral one, unlike the reindeer, which has a ventral outgrowth located below the dorsal outgrowth. As a result of our research, it was found that the gluteal-biceps muscle of the noble spotted deer is fleshy, the largest among the thigh muscles, forms a convex (rounded) contour in the gluteal region, filling most of the gluteal region. Extending in the distal direction, the muscle participates in the formation of the lateral and caudal contour of the thigh, and on the lateral surface of the lower leg forms a flattened tendon, following from the lateral surface of the kneecap, the cranial crest of the tibia to the calcaneal mound of the flattened. The established structural communications of the studied muscles may reflect their functional relationship. The data obtained are reference in assessing the biomechanics of the stato-locomotor act in representatives of the reindeer, as well as in the diagnosis of damage to the musculoskeletal system.

Evolution of anther connective teeth in sages (Salvia, Lamiaceae) under bee and hummingbird pollination

Salvia (Lamiaceae) is a sub-cosmopolitan genus of about 1000 species that often employ a “staminal lever mechanism” that is thought to have spurred species diversification within the genus. The function and evolution of ventral outgrowths or connective teeth, associated with the lever mechanism in some species of Salvia, is often unclear despite the wealth of pollination observations across the genus and the major role that pollinators play in driving diversification within the genus. We document the role of these teeth in pollination studies of bee-pollinated Salvia farinacea, examine connective teeth across other bee- and hummingbird-pollinated species of New World subg. Calosphace, and provide an evolutionary scenario for the connective teeth in context of the staminal lever. Our observations show that the larger teeth function as pressure points at the floral entrance and, when pressed by a pollinator, facilitate movement of the lever. Multiple shifts in pollinator within subg. Calosphace may have resulted in further modifications of the connective and possible further losses and independent origins of connective teeth in Calosphace. Other distantly related subgenera (e.g., Sclarea, Glutinaria) display morphologically and spatially different protuberances on the connective, suggesting that connective teeth only evolved near the base of subg. Calosphace.

Cytological, histochemical, and ultrastructural study of human foetal liver of various gestation with future implications in segmental resection: an anatomical perspective.

The liver is the largest gland of the gastrointestinal tract having both exocrine and endocrine functions. Developmentally it arises as a ventral outgrowth from the gut endoderm during 3rd week of intrauterine life. The foetal liver is very important because of its synthetic and hemopoietic potential. The present work aimed to see the detailed histogenesis and development of the foetal liver by cytological, immunohistochemical and ultrastructural study. The liver tissue of nine aborted foetuses of various gestational age were studied. For cytology: special stains like Masson trichrome, periodic acid Schiff and reticulin were used, immunohistochemical staining was performed with triple antibodies (c-myc, Ki-67 and Ber-H2), and for ultrastructure: aluminium mounted specimens were coated with gold and argon gas and observed under scanning electron microscopy (EM). Cytology and immunohistochemistry showed the development of duct patterns and hemopoietic patterns in all stages of fetogenesis. The ductal plate was marked by the layer of dark brown staining cells at the edge of two portal tracts. The haemopoietic cells with sinusoids and aggregation of hepatocytes were observed in the early weeks of gestation. EM showed tree-like branching of a portal canal depicting hepatic segmentation of foetal liver. The organizational changes in lobular pattern, duct pattern, and microstructure of liver during fetogenesis are very crucial to achieve the adult morphology in feature. Histogenesis of the foetal liver follows a multistep process depending upon the gestational age, any deviation from normalcy may lead to structural and functional abnormality later in life.

Три новых клейстокарпных вида родов Tortula и Microbryum (Pottiaceae, Bryophyta)

Three new cleistocarpous species belonging to the genera Tortula and Microbryum were found among specimens in herbaria LE and MHA identified as Pterygoneurum kozlovii (redefined as Pterygoneurum sibiricum), Tortula acaulon, Microbryum vlassovii and Microbryum curvicollum. The new species Tortula arenaria found in collections from the Republic of Dagestan is similar to M. curvicollum in having curved costa but differs in large and roughly papillose spores (vs. smal ler and smooth in M. curvicollum), branched papillae (vs. simple papillae in M. curvicollum). The new species Microbryum lydiae found in collections from the Republic of Armenia is similar to M. vlassovii in having ventral outgrowths of costa presented as elongated parenchymatous cells but differs in long-mammillose leaf lamina and costa cells (long-mammillose-papillose in M. vlassovii); smaller, warty papillose spores (vs. larger, streaky papillose in M. vlassovii). The new species Tortula irinae is similar to cleistocarpous species of the genus Pterygoneurum in having ventral outgrowths of costa, but differs in outgrowths presented as a pad of large, elongated parenchymatous cells (vs. as low lamellae of several rows of small cells in height in P. kozlovii and high lamellae in P. sibiricum). By ventral outgrowths of costa presented as elongated parenchymatous cells it is also similar to some species of the genus Microbryum, from which it differs in leaf lamina and costa cells with several branched papillae (vs. long-mammillose-papillose leaf lamina and costa cells with one branched papilla in M. vlassovii and long-mammillose leaf lamina and costa cells with one large mammilla in M. lydiae). Tortula irinae resembles T. acaulon in having cleistocarpous immersed capsule. Tortula acaulon is a highly variable species represented by several morphotypes of uncertain taxonomic status but strongly differing in many characters of sporophytes and gametophytes. The most important diagnostic characters are the degree of papillae expression and the shape of leaf and costa papillae. By the degree of papillae expression and the shape of papillae, several morphotypes of T. acaulon were revealed: 1 – morphotype without papillae, 2 – morphotype with simple papillae, 3 – morphotype with branched papillae. Tortula irinae differs from T. acaulon morphotypes in having ventral outgrowths of costa lacking in T. acaulon morphotypes. How ever, of all T. acaulon morphotypes studied, T. irinae can be most probably confused with T. acaulon “branched papillae morphotype” in having strongly branched papillae of costa and leaf cells but easily differing in shape of ventral costa cells protruding as a pad of large, elongated parenchymatous cells in T. irinae vs. ventral costa cells smaller, not protruding in T. acaulon “branched papillae morphotype”. Tortula irinae is widespread in Asian part of Russia [Chukotka Autonomous Area, Republic of Sakha (Yakutia), Trans-Baikal Territory]. It was also found in kept in LE moss collections from Asia (Khazakhtan, Mongolia) and Europe (Ukraine).

Genomic architecture of Shh-dependent cochlear morphogenesis.

The mammalian cochlea develops from a ventral outgrowth of the otic vesicle in response to Shh signaling. Mouse embryos lacking Shh or its essential signal transduction components display cochlear agenesis; however, a detailed understanding of the transcriptional network mediating this process is unclear. Here, we describe an integrated genomic approach to identify Shh-dependent genes and associated regulatory sequences that promote cochlear duct morphogenesis. A comparative transcriptome analysis of otic vesicles from mouse mutants exhibiting loss (Smoecko ) and gain (Shh-P1) of Shh signaling reveal a set of Shh-responsive genes partitioned into four expression categories in the ventral half of the otic vesicle. This target gene classification scheme provides novel insight into several unanticipated roles for Shh, including priming the cochlear epithelium for subsequent sensory development. We also mapped regions of open chromatin in the inner ear by ATAC-seq that, in combination with Gli2 ChIP-seq, identified inner ear enhancers in the vicinity of Shh-responsive genes. These datasets are useful entry points for deciphering Shh-dependent regulatory mechanisms involved in cochlear duct morphogenesis and establishment of its constituent cell types.

Proboscis ornamentation as a diagnostic character for the Anoplodactylus californicus-digitatus complex (Arthropoda: Pycnogonida) with an example from the Anoplodactylus eroticus female

Females of the Indo-Pacific species Anoplodactylus eroticus (Arthropoda: Pycnogonida: Phoxichilidiidae) are described for the first time. The presence of peculiar ventral outgrowths or protuberances on the female proboscis of A. eroticus and 13 other Anoplodactylus species motivates an evaluation of a californicus-digitatus complex, based on external morphology and species distribution. The anatomy and development of proboscis protuberances is assessed using scanning electron microscopy (SEM), Nomarski optics, and flourescence microscopy. External morphology of A. eroticus is compared to that of apparently related species. An identification key for the 14 species of Anoplodactylus with females bearing a proboscis with ventral protuberances is provided here as an identification tool.

Morphology of a novel glandular epithelium lining the infrabuccal cavity in the ant Monomorium pharaonis (Hymenoptera, Formicidae)

A novel glandular epithelium lining the infrabuccal cavity and anterior pharynx is described in both workers and queens of the pharaoh's ant Monomorium pharaonis. The infrabuccal cavity, connected with the buccal tube, forms a ventral outgrowth of the anterior pharynx, and as such displays the tegumental lining with a cuticle and an epithelial layer. In its dorsal region, the cavity's epithelium reaches a thickness of approx. 11–12 μm in both workers and queens, which is considerably thicker than the epithelium lining the rest of the infrabuccal cavity. Also the possible role of the infrabuccal gland is discussed.

Myxobolus buckei sp. n. (Myxozoa), a new pathogenic parasite from the spinal column of three cyprinid fishes from the United Kingdom.

Myxobolus buckei sp. n. is described from the spinal column of Leuciscus cephalus (L.), Rutilus rutilus (L.) and Abramis brama (L.) from freshwater rivers in the North of England. The plasmodia develop within the remnants of the embryonic notochord in the intervertebral spaces. The spores are large, measuring (in microm) 14.0 +/- 0.7 x 11.5 +/- 0.6 (mean +/- SD), smooth, round to ellipsoid in valvular view with several sutural edge markings. The polar capsules are pyriform and of equal size, measuring 7.5 +/- 0.5 x 4.2 +/- 0.2 (mean +/- SD), with 11-12 turns of the polar filament arranged perpendicularly to the longitudinal axis of the polar capsule. The parasite has a large intercapsular appendix and large iodinophorous vacuole. The parasite can be differentiated from all known species of Myxobolus Bütschli, 1882 by a combination of the morphological characters defined. Infected fish show marked longitudinal compression of the body compared to uninfected individuals of the same year class, a feature which is pathognomonic for the disease. Histologically, host responses ranged from mild hypertrophy of the zygapophyseal process and expansion of the intervertebral membrane to complete hypertrophy and fusion of the vertebrae. Prominent notochord is present in the intervertebral spaces of infected fish and sporogony of the parasite leads to a vigorous focal inflammatory response involving proliferating fibroblast and osteogenic cells. The parasite causes a radial expansion of the centra and extensive dorsal and ventral outgrowths of the vertebrae leading to compression of the spinal cord and blood vessels running through the neural and haemal spines respectively. The parasite is considered highly pathogenic to juvenile cyprinids.

DecapentaplegicOverexpression AffectsDrosophilaWing and Leg Imaginal Disc Development andwinglessExpression

We have used the GAL4-UAS expression system to increase the level of expression of theDrosophilagenedecapentaplegic(dpp) in a pattern approximating its normal pattern in leg and wing imaginal discs. Intermediate increases ofdppexpression have little effect in wing discs but high levels ofdppoverexpression lead to reduction of the scutellum and duplication of posterior wing structures. In leg discs intermediate increases cause supernumerary outgrowths of ventral leg structures in the anterior–ventral region. Greater increases ofdppexpression cause the loss of ventral leg structures with the concomitant fusion of left and right dorsal forelegs. The defects observed in both legs and wings appear to arise through dose-dependent effects ofdpponwingless(wg) expression. A high level ofdppoverexpression in the wing disc causes reduction ofwgexpression in the presumptive scutellar region, consistent with the subsequent reduction of the scutellum. An intermediate increase ofdppexpression in leg discs induces the expansion ofwgexpression into the ventral outgrowths. At higherdppexpression levels, ventralwgexpression in leg discs is eliminated, consistent with the loss of ventral leg cuticle. In the leg disc end knob and in the wing margin primordium, wherewganddppcooperate in producing distal outgrowth,dppoverexpression has no detectable effect either on patterning or onwgexpression. We propose that a critical role fordppin other regions of the leg and wing discs is to reduce or block the expression ofwg.This role ofdppis supported by the observation that ectopicwgexpression is detected in imaginal discs wheredppsignaling is compromised by lowering the activity of one of its receptors,tkv.This antagonism betweendppandwgexpression may be critical to assigning only one disc region as the distal organizer.

The fine structure and function of the cephalic appendages of the branchiuran parasite, Argulus japonicus Thiele

The fish parasite Argulus japonicus Thiele (Crustacea: Branchiura) has recently been introduced into Britain and is now established in the wild. A. japonicus , an ectoparasite attaching to, and feeding on, the skin of its host, is a potentially serious pathogen of native freshwater fishes. The anatomy of the attachment and feeding structures is described using light and electron microscopy. The primary attachment organs are the suckers derived from the maxillules. The extrinsic musculature of the suckers comprises two major muscle groups: the suction muscles which insert on the floor of the sucker and generate suction, and the cup muscles which control the orientation and movement of the sucker as a whole. The inner wall of the sucker cup comprises two hoops of thickened cuticle and provides the rigidity necessary to prevent the sucker from collapsing. These hoops are hinged to allow extra movement of the distal hoop plus its marginal m em brane when forming a seal onto the surface of the host. Numerous mucous glands are present in the floor of the sucker. The elongate mouth tube represents a ventral outgrowth of the head bearing a small labrum and labium distally. The homology of the labium is confirmed by the arrangement of its paired muscles, which originate on the undersurface of the ventral cephalic tendon and pass down through channels in the suboesophageal ganglion. The labrum lacks muscles. The ontogeny of the mouth tube, the adult m andibular musculature and the possible feeding mechanism are described. The preoral spine lies in the ventral midline of the body anterior to the mouth tube. It consists of a tapering spine carried on a long eversible sheath. When fully retracted the spine and sheath virtually disappear into the body. As the spine retracts the cuticle of the proximal sheath becomes inverted. The epithelium beneath this sheath cuticle is syncytial and is separated from the cuticle-lined, central duct of the spine by a fluid matrix which can be displaced as the spine is retracted. The fluid matrix appears to be secreted by the epithelial cells of the sheath cuticle. Retraction is by means of paired retractor muscles which originate dorsal to the midgut and pass down through the nerve ring. These muscles shorten to about 25% of their maximum length during extreme retraction.

The allantois of the North American opossum (Didelphis virginiana) with preliminary observations on the yolk sac endoderm and trophectoderm.

During the middle of prenatal day 10, the opossum allantois forms as a ventral outgrowth of the hindgut. By day 11 it appears as a large, fluid filled sac and by the middle of day 12 (just prior to birth) it reaches its maximal development. The simple squamous epithelium lining the allantois consists of only one cell type that often contains numerous filaments in the apical cytoplasm. At the luminal surface, the apices of the cells are united by junctional complexes and desmosomes are present between adjacent cells. The luminal surface is irregular, whereas laterally and basally the cell membranes show few if any infoldings. Mitotic figures and presumptive degenerating cells occasionally occur in the allantoic epithelium which rests on a delicate basal lamina. The allantois is covered by a simple squamous mesothelium that lacks a distinct basal lamina. Between the two epithelial sheets lie mesenchymal cells, collagen fibers, and blood vessels. No specializations of cell membranes were noted in either of the epithelial layers. The yolk sac endoderm consists of a single layer of squamous cells whose cytoplasm contains scattered profiles of rough endoplasmic reticulum and mitochondria. Extensive lateral and basal infoldings of the plasmalemma were not observed in these endodermal cells. The morphology of the trophectodermal (trophoblastic) cells indicates a cell type that is active in the transport of materials. Since the endodermal cells that line the allantois lack morphological features that would suggest the presence of mechanisms for transport or exchange, and because they remain relatively unchanged throughout pregnancy, it is thought that the allantois functions primarily in the storage of urinary wastes during prenatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the Queensland Lungfish, Neoceratodus forsteri (Krefft).

The lung of Neoceratodus forsteri consists of a single elongated sac dorsal to the gut and attached firmly along the dorsal mid-line in the region of the vertebral column. It communicates with the gut through the pneumatic duct which opens ventrolaterally via the glottis, on the right side of the pharynx. The embryological origin of the lung as a ventral outgrowth from the gut is reflected in the marked similarity between their tissues, and in the unusual configuration of the duct and blood vessels. Internally, the lung is divided into compartments formed by septa resulting from infolding of the walls. These compartments are further subdivided to form a spongy alveolar region. In this region of increased surface area run blood capillaries in proximity to the respiratory medium, close enough to allow gaseous exchange with it. Filling the lung is accomplished by a buccal force-pump, as in Amphibia, consisting of the hyoid apparatus and the muscular walls of the buccal cavity. Exhalation of air is effected by contraction of the smooth muscle components of the lung, assisted by its natural elasticity provided by elastin fibres present in both connective tissue and smooth muscle. The structure of the lung, its spongy walls, vascular supply with capillaries close to the air space, open pneumatic duct, regular exchange of air at the surface of the water, and the ability of the fish to survive out of water if kept moist, all point to the function of the lung as a respiratory organ. This is borne out by lung-gas analyses which consistently show lower oxygen level compared with air.

Experimental Demonstration of Tongue Muscle Origin in Chick Embryos

ABSTRACT Since in all classes of vertebrates the tongue muscles are innervated by nerve XII, a segmental nerve of the occipital region, it is usually argued on this criterion alone that they originate from occipital myotome tissue. Descriptive evidence in support of this generalization is, however, far from adequate. The most complete accounts that exist refer to one amphibian and two reptile species. In the amphibian Necturus, Platt (1897) observed that ventral outgrowths of the 3rd and 4th occipital myotomes became tongue muscles, and Edgeworth (1935) has described the development of tongue muscles in the reptiles Sphenodon and Lacerta, from ventral parts of two occipital and two cervical myotomes, all innervated by nerve XII. In avian and mammalian embryos, however, early muscle rudiments are extremely difficult to recognize with any certainty histologically. Although Butcher (1929) and Bates (1948) have observed ventral outgrowths of occipital myotomes in rat and cat embryos, and Bates claimed that these are recognizable as tongue muscle primordia in later stages, both these authors drew their conclusions from relatively few fixed specimens, and in Bates’s photographs the rudiments are not nearly as distinct as his diagrams suggest they are. The same criticism applies to Hunter’s description (1935) of occipital myotome rudiments that apparently develop into tongue muscles in the chick. The only other detailed description of tongue muscle development in birds is that of Kallius (1905) who dealt with advanced stages when the muscle primordia are already in situ.

On the Assignment of the Class Pogonophora to a Separate Phylum of Deuterostomia Brachiata A. Ivanov, Phyl. Nov.

JOHANSSON (9), having recognized that Lamellisabella belongs to a special class Pogonophora, has placed it close to the Phoronidea. However, the trunk of the latter represents a greatly extended ventral outgrowth of the larva and does not correspond to the trunk of the Pogonophora. Besides this, Phoronidea possess only two pairs of coeloms, gonads not separated from the coelom, and a pair of lateral nerve trunks. Much nearer to the truth is the opinion of Dawydoff (4) and Beklemishev (1) who place the Pogonophora near the Hemichorda. Now, when the organization of the Pogonophora is clear in its main traits, one can point out a series of characters in common with the Hemichorda. Such are: the composition of the body of three segments, the single anterior coelom, the pericardium, the coelomoducts of the first segment, the situation of the gonads in the trunk segment and their separation from the coelom, the dorsal nerve trunk and the epithelial position of the nervous system. Besides this, a peculiarity in common with the Enteropneusta is the secondary metamerization of the elongated trunk section, although in Pogonophora secondary metamerization affects also other organs. Notwithstanding this it would be wrong to include Pogonophora as a subphylum in the Phylum Hemichorda, as is done by Beklemishev (1). This is contradicted by the belonging of the tentacles to the first and not to the second segment as in Pterobranchia, by the strong development of the anterior coelomoducts which have an excretory function, by the absence of these organs in the second segment and by their development in the trunk section. Among the distinctive characters of Pogonophora are: the development of the brain in the first and not in the second segment, the development of the heart from the ventral and not from the dorsal vessel, and finally the strong cuticularization of the integument. The absence of gill slits and of a notochord cannot serve as distinctive characters because of the secondary reduction of the digestive tract. A series of peculiarities of the organization of Pogonophora developed under the influence of sedentary life. To these belong: the ability to secrete a protective tube, the extraordinary length of the trunk and the substitution of the digestive tract by a peculiar tentacular apparatus which performs the functions of accumulating, digesting and resorbing the food (7). All this forces us to regard the Pogonophora as an independent phylum of Deuterostomia which I propose to call Brachiata. The Phylum Brachiata may be characterized as follows. The body of these lower Deuterostomia consists of three segments of which the two anterior ones form by fusion the anterior section of the body. The first segment contains a single coelom with a pair of excretory coelomoducts, and forms the dorsal cephalic lobe and the tentacular apparatus. The second segment is without coelomoducts. The trunk segment is greatly elongated and contains a single pair of gonads; its coelomoducts function as gonoducts. The integument is cuticularized; ciliated epithelium is retained only partially. The brain belongs to the anterior segment; from it the dorsal nerve trunk originates. The entire nervous system occupies an epithelial position. The circulatory system consists of a dorsal and a ventral vessel connected anteriorly by a system of vessels of the tentacular apparatus. There is a muscular ventral heart which some-

LATERAL PHARYNGEAL DIVERTICULA AS A CAUSE OF DYSPHAGIA

A comparatively rare cause of dysphagia not ordinarily considered in differential diagnosis is that of lateral pharyngeal diverticula. Recently we have had two examples of this disorder. In this condition the diverticula project anterolaterally from the hypopharynx at about the level of the pyriform sinuses. We include herein a brief survey of the embryology of this condition. The lateral surfaces of the neck of the embryo become indented by four bilaterally-paired branchial grooves during the fourth to fifth weeks of embryonic life. Concurrently, four bilateral pairs of branchial or pharyngeal pouches arise internally from the lateral walls of the pharynx. These grooves and pouches correspond and lie opposite each other. Each pair is separated from the next by the branchial arches. An unpaired median outgrowth also appears in the floor of the pharynx. The single ventral outgrowth is the thyroid diverticulum, which becomes the thyroid gland. The first pharyngeal pouch

The liver in relation to protozoal infections

I thought that before writing this paper I should consult some standard works on the liver and its diseases ; what was my surprise when I found that not a single word in these books referred to protozoal diseases, in spite of t h e fact that malaria, for instance, is the greatest single cause of morbidity in the human race ; so perhaps this approach to the subject is not inopportune. I do not intend to discuss, this evening, all the Protozoa Which affect the liver ; in, fact, I am excluding nearly all the organisms which cause extensive damage to its substance, such as Entamoeba histolytica which gives rise to amoebic abscesses, or Histomonas meleagridis producing blackhead in turkeys or Leishmania donovani, the cause of kala-azar. The group of Protozoa that I am going to refer to are the Sporozoa, the class which includes the malaria parasites. Recent work on the life history of these organisms---chiefly by the President of our Society--has brought the liver very much into the limelight. First I must say a little about the organ itself. The liver is the largest gland in the body and is indispensable to life. It is composed of lobules about 2 mm. in diameter, each lobule consisting of columns of parenchyma cells. Around each lobule is connective tissue wherein travel branches of the portal vein, hepatic ar tery and bile duct. In the centre of each lobule is a branch of the hepatic vein. The two circulations meet in the sinusoids between the columns of liver cells. The sinusoids are lined by the strongly phagocytic Kupffer cells and ordinary endothelium ; it is improbable that the blood comes into direct contact with the parenchyma itself. The liver develops as a ventral outgrowth of the endoderm of the duodenal portion of the mid-gut. It projects itself into a mass of undifferentiated mesoderm via which it becomes vascularized and from which it obtains its connective tissue framework. These two elements--the mid-gut endoderm and

8. On the Segmentation of the Occipital Region of the Head in the Batrachia Urodela

Summary.The chief contents of this paper may be summarised as follows. Three occipital segments occur in the head of Amblystoma. Of the three somites developed in these, the first forms no muscle and disappears early the second forms a myotome divided into dorsal and ventral portions, of which the former alone persists, fusing with the myotome next behind. The myotome of the third segment persists dorsally, that of the first trunk‐segment combines with it to form the temporal longitudinal muscle supplied in the adult by the first spinal nerve. The glosso‐pharyngeal nerve belongs to the first metaotic segment and has no ventral root. To the second segment belongs the vagus root, with which seems to be combined the ganglia of the next two nerves. No ventral root was found in the second segment; but a ventral root occurs in the Iast metaotic segment in early stages of development. The first spinal issues from between the skull and first neural arch as a ventral root only; it joins the second spinal to form the hypoglossal nerve supplying muscles derived from ventral outgrowths of the second. third, and fourth myotomes. The basilar plate of the skull is formed by a backward growth of the trabeculæ: meeting a forward growth of the base of the orcipital arches. It fuses with the auditory capsules, and with the praæoccipital arches developed in the septum between the first and second myotomes. The occipital arches arise in the septum between the second and third myotomes. There is no evidence of the disappearance of segments behind the vagus, and no valid objection to the view that the hind limit of the skull may shift backwards or forwards in the course of phylogeny. At the same time there is no reason to suppose that the ancestors of the Amphibia had more than three occipital segments, when the occipital condyle became clearly defined.

On the Development of Peripatus Novæ-Zealandiæ

On the Development of Peripatus Novæ-Zealandiæ