Structure Of Gametes Research Articles

Fertilization in the white chiton, Stenosemus albus, with implications for its phylogenetic position

Gamete structure and fertilization biology of the white chiton, Stenosemus albus (L., 1767), were studied with light and electron microscopy. Sperm structure was found to be similar to other Chitonina, but acrosomes are homogeneous in this species, like those of Chaetopleura apiculata (Say in Conrad, 1834). The egg of S. albus is covered by long spines with hooked tips. The bases of spines are perforated along their perimeters by a series of pores that provide sperm with direct access to the vitelline layer. This feature appears to be plesiomorphic and characterizes also Chaetopleura but not most Chitonina, which have a continuous dense layer overlying the hull. Beneath the vitelline layer, the egg membrane is formed into a series of cups with raised edges elaborated into microvilli that coincide with the bases of hull spines. Free-spawned sperm of S. albus were able to find the egg and penetrate a pore in the hull within 20 s. Evidence presented here, and previously, indicates that S. albus shares a number of key characters in common with Callochitonidae, which is a basal family within Chitonida. Taken together, the evidence suggests that Stenosemus belongs to a basal taxon within Chitonina, outside the Ischnochitoninae, in which it is currently placed.

Fertilization biology and the evolution of chitons*

Studies of gamete structure and fertilization biology have revealed much about the phylogeny of molluscs. Recent studies of fertilization in chitons support the view that the basal order of chitons, the Lepidopleurida, fertilize eggs, as most molluscs do, by fusing the entire sperm with the egg and transferring chromatin, mitochondria, and centrioles into the egg cytoplasm. However, current evidence suggests that all members of the order Chitonida inject only chromatin into the egg. These chitons, which include the controversial family Callochitonidae, share a series of synapomorphic characters based on their fertilization biology that makes them unique. Current evidence suggests that Callochitonidae are basal to this order and sister taxa to the remaining Chitonida, which have been divided into two suborders, the Chitonina and Acanthochitonina. New evidence indicates that Chitonina have at least two different mechanisms for penetrating the egg. One group of species has pores in the egg hull (e.g., Chaetopleura apiculata (Say in Conrad, 1834) and Stenosemus albus (Linnaeus, 1767), whereas a second group has a continuous dense layer on the surface of the egg hull that is digested by the sperm (e.g., Rhyssoplax tulipa (Quoy and Gaimard, 1835) and Stenoplax conspicua (Pilsbry, 1892)). However, the genus Ischnochiton Gray, 1847 appears to be polyphyletic, as several species have distinctive characters that typify other genera or families. In particular, this genus needs to be re-evaluated using modern morphological and molecular methods. All of the Chitonina have spiny-hulled eggs with narrow bases and are quite different from the second suborder, Acanthochitonina, which is characterized by large-hull cupules with wide bases. Within Acanthochitonina, some species have open-hull cupules, whereas most have closed ones. Open-cupule species lack micropores in the hull for sperm entry, whereas several closed-cupule species exhibit micropores between hull cupules. These features of the egg are accompanied by alterations in sperm structure, such as position of the mitochondria and structure of the basal body, acrosome, and flagellum. Knowledge of the gamete structure of individual species and their fertilization biology, as demonstrated here, provides a different series of characters that can help avoid mistakes that are inherent during early development of new methods, such as molecular analyses. New details of fertilization biology have made it possible to revise preliminary analyses and provide an updated phylogeny of chitons, which differs in some important respects from other recent publications.

Sex cells and reproduction in the diatom Nitzschia longissima (Bacillariophyta): discovery of siliceous scales in gamete cell walls and novel elements of the perizonium

I. Kaczmarskam, N.A. Davidovich and J.M. Ehrman. 2007. Sex cells and reproduction in the diatom Nitzschia longissima (Bacillariophyta): discovery of siliceous scales in gamete cell walls and novel elements of the perizonium. Phycologia 46: 726–737. DOI: 10.2216/07–04.1We examined the fine structure of gametes and the auxospore wall in the heterothallic pennate raphid diatom Nitzschia longissima (sensu Karsten 1897). The presence of scales in the gamete wall of both sexes is demonstrated for the first time for a pennate diatom species. Silica in scales was documented by energy dispersive x-ray spectroscopy. This finding supports our earlier hypothesis that scales are present in pennate sex cells more often than previously considered and reflect their evolutionary relationship to scale-bearing ancestors. In addition, the auxospore was shown to contain both transverse and longitudinal perizonia as well as longitudinal bands with fimbriate margins. Longitudinal bands are also novel components of a pennate auxospore. All these structures are either difficult to resolve or irresolvable in light microscopy (LM), clearly demonstrating that LM is not sufficient to investigate diatom sex cell structure. The sexual process employed by N. longissima is compared to its congenerics. Unlike other species from this genus, our diatom is morphologically and behaviourally anisogamous. In addition, the copulation of gametangia is not aided by copulation tubes, papillae or copulation jellies. Therefore, sexual reproduction in N. longissima shows little similarity to that of the few other species in the genus Nitzschia thus far examined.

The population structure of rural settlements of Sakha Republic (Yakutia): Migration

Migration and gametic structure have been analyzed in rural population of Sakha Republic (Yakutia). The populations studied differ from one another in the migration rate and direction, which are determined by the socioeconomic development of the regions and ethnic composition of settlements. A high rate of long-distance migrations and a low rate of migrations within uluses (districts) are characteristic of regions with well-developed industry and transportation and are more characteristic of immigrant than indigenous populations. In rural regions, migrations within uluses are more prevalent. The gametic structure of the youngest age group does not always correspond to the migration activity of previous generations. The migration effectiveness values (the correspondence of migration flows to the gametic structure depending on the geographic origin of the gametes) are different for men and women.

Genetic Demographic Description of the Ust-Aldan Rural Population of Sakha Republic (Yakutia): Migrations and Marriage Structure

Migrations, dynamics of the gametic structure of rural populations, and marriage structure with respect to birthplaces and inbreeding estimated from isonymy have been studied in the Ust-Aldan ulus (administrative district) of Sakha Republic (Yakutia). The villages studied (Byadi, Dyupsya, and Cheriktey) are characterized by intense migration; however, the migration radius is small (most migrations occur within the district). The rural populations studied differ in the intensities and directions of gamete flows and their dynamics. There is no substantial gamete flow into the Ust-Aldan population from outside Sakha Republic. About 50% of marriages contracted in this population are homolocal (between residents of the same district); the endogamy is low (15%). In most cases of heterolocal marriages (contracted between residents of different districts), one of the spouses is a local resident. The inbreeding estimated from isonymy is FTT = 0.002930 in Yakuts; it is mainly accounted for by the nonrandom component (FIS = 0.002232 and FST = 0.000700).

Ultrastructure of the biflagellate gametes of Collinsiella cava (Ulvophyceae, Chlorophyta)

SUMMARY The fine structure of the biflagellate gametes of Collinsiella cava (Yendo) Printz was investigated in detail to clarify the species's taxonomic and phylo-genetic position. Gametes are covered by small square scales with no distinct substructure. The chloroplast of the gamete includes an eyespot comprised of two layers of globules, and a pyrenoid that is traversed by one or a few thylakoids. Basal bodies overlap at their proximal ends and are offset in a counterclockwise orientation. Each basal body has a small bipartite terminal cap, a prominent proximal sheath comprised of two unequal subunits and a circular element situated at the cartwheel portion. A distal fibre, a connecting fibre and linkage between proximal sheaths connect the two basal bodies. Microtubular roots are comprised of two dexter (d) roots, subtended by the system I fibre, and two sinister (s) roots. Gametes have a single rhizoplast which extends parallel to one of the two d roots and extends to the mating structure. The ultrastructure of Collinsiella gametes is very similar to that of Mono-stroma and other members of the Ulotrichales, Ulvophyceae, and we concluded that the genus Collinsiella should be treated as a member of the Monostromat-aceae. The planozygote has four basal bodies, eight microtubular roots and two eyespots always situated at the same face of the cell. From observations of the planozygotes, the position of the mating structure relative to the flagellar apparatus is not consistent, but converse, between two mating types. A comparison of the location of the mating structure in Chlamydomonas and other green algae is presented.

Morphology of gametes in five species of far-eastern chitons

Summary Sperm development, structure of the gametes and some aspects of fertilization in the far-eastern chitons Leptochiton assimilis, Deschayesiella curvata (fam. Leptochitonidae), Tonicella undocaerulea (fam. Tonicellidae), Mopalia retifera (fam. Mopaliidae) and Ischnochiton hakodadensis (fam. Ischnochitonidae) are described by transmission electron microscopy. In the testis spermatogenetic cells are closely associated with auxiliary cells, which are structurally identical to those of other mollusks and probably have a nutritive function. Spermatogenesis in all species did not differ from that of chiton species already studied and it was confirmed that an acrosome is formed from the Golgi apparatus during spermiogenesis. The spermatozoa of all studied species have a structure that is typical for chitons. The sperm of Deschayesiella curvata (Order Lepidopleurida) have a head consisting of a large acrosome and nucleus with an (3.5–4.2μm) asymmetrically positioned anterior extension. The centrioles are surrounded by five spherical mitochondria. The spermatozoa in Tonicella undocaerulea, Mopalia retifera and Ischnochiton hakodadensis (Order Chitonida) have a small acrosome and a nucleus with long thin anterior extension; mitochondria are lateral to the nucleus. There are considerable interspecific differences in the structure of egg envelopes. Our results, along with those of other workers, show that gamete structure of chitons is specific to each family. A cortical reaction which results in formation of a fertilization envelope takes place in the egg of chitons after fertilization.

Spawning and management of gametes, fertilized eggs and embryos in Siluroidei

The structure of gonads and gametes is highly diversilied in siluroid fishes; in some groups the testes are composite with an anterior part formed of spermatogenetic tissues and the posterior part of seminal vesicles which may or may not store spermatozoa. For catfish species of aquacultural interest, ovaries present the same general morphology as in other teleosts with oviducts. Spermatozoa are biflagellated in the Channel catfish (Ictalurus punctutus) and monoflagellated in the European catfish (Silurus glanis) and African catfishes (Clarias gariepinus, Heterobranchus lingijilis). The egg size shows considerable intergroup differences, from 0.8-1.2 mm in some Pimelodidae and Clariidae up to 15-20 mm in Anidae. In numerous cases, the eggs are adhesive and develop either a surrounding sticky layer (Ictulurus, Chrysichthys, Silurus) or an adhesive attachment disc (Clarias, Heterobranchus). Fertilization is in general extemal but intemal fertilization is reported in some species. The annual sperm production was measured in European catfish and Channel catfish as 1.7 x 10 and 1.8 x 10 spermatozoa.kg-' body weight, respectively. In females, the fecundity ranges from about 50 eggs per spawn in ariids up to more than 100000 eggs.kg-' body weight, e.g. in pimelodids and clariids. A large variety of controlled reproduction systems are found in the siluroids. In some cases (Ictulurus, Chrysichthys, Hoplosternuin), spawning oceurs naturally in ponds or tanks provided that adequate spawning substrates are available; fertilized eggs are collected immediately after spawning and placed into incubators until hatching. But for most species, although natural or seminatural spawning could be achieved in captivity, the tendency at the present time is to develop techniques using hormonal-induced ovulation and artificial insemination in order to control the various steps of reproduction and to allow gamete preservation and manipulation. Oocyte maturation and ovulation or spermiation can be induced in many species by a large variety of hormones (GnRHs, fish gonadotropins, hCG, vanous steroids etc). Some information is available on gamete biology and preservation. Sperm motility is short-lived, not exceeding 70-80 s of fonvard movement as in most other freshwater teleosts. A peculiarity of the European catfish sperm is the activation by urine during sampling which could be prevented by direct collection in an immobilizing solution (NaCI 200 mM, Tris HCl 30 mM, pH 7.0). Spermatozoa cryopreservation was successfully attempted in several species. Ova generally survive only a few hours after ovulation and fertilization must be camed out soon after. Methods for gamete collection, insemination and incubation of eggs are descnbed for the most widely cultured siluroid species.

Ultrastructure of sperms in bivalve molluscs of the Mytilidae family

Summary The sperm structure of five external fertilizing bivalve molluscs pertaining to the Mytilidae family is compared. Apart from examining if such gamete structure conforms to the primitive sperm form of the type I predicted by Franén, a major aim of the study is to compare the development and structure of some organelles whose evolution among the bivalve sperms has also been associated with the style of fertilization (whether external or within brooding chambers where the retained eggs are fertilized). Observations are specially focused on examining the existence of the acrosome, its morphology and the way in which it develops as well as on the pattern of condensation of the nucleus. Finally, the morphology of the mitochondria, conforming the mid-piece, is also examined. The sperms studied conform to the primitive general type proposed for external fertilizing species as well to the morphological pattern presented by other free-spawning bivalve molluscs. A well developed acrosome is observed, supporting the contention that such organelles tend to persist among the typical broadcast fertilizer bivalves, probably linked to egg coat structure variations. This acrosome, however, appears as the most variable organelle, with diversity of shape, size and inner structure, particularly with respect to the number of compartments structuring it. Most of the species examined show absence of an axial rod as part of the apparatus making up the acrosome, a feature considered primitive by some authors; the exception is Mytilus chilensis where such structure does differentiate. This characteristic—also presented in the literature about other Mytilus species—adds to other traits shared by the sperms of this mytilid genus, thus also showing the potential value that sperm morphology could have to substantiate the studies of taxonomic affinities among these bivalve molluscs.

The Reproductive Biology of Kauri (Agathis australis). II. Male Gametes, Fertilization, and Cytoplasmic Inheritance

The reproductive cycle of Kauri (Agathis australis) lasts about 18 mo in New Zealand. Pollination occurs in October and seeds are mature in March. Prefertilization stages were described in a previous study. In October, about 1 yr after pollination, megagametophytes matured. Pollen tubes had penetrated and branched around the megagametophyte the previous March. The tube cell contained several prothallial cells, a tube nucleus, and a large body cell. The tube cell and body cell contained many lipid droplets. The egg lacked lipid droplets. The body cell divided, forming two large equal-size male gametes sharing a common combined body-cell and tube-cell cytoplasm. Male nuclei included some body-cell cytoplasm and organelles. In mid-October pollen tubes penetrated the megaspore wall and central neck cells, and then released their contents into the egg cytoplasm. One male gamete and a mass of paternal cytoplasm moved to the egg nucleus. As the male and egg nuclei fused, the mass of paternal cytoplasm, distinguished by the many lipid droplets, settled over and enshrouded the zygote nucleus. Egg perinuclear cytoplasm was pushed aside and the neocytoplasm was made up of paternal cytoplasm originating from some tube-cell cytoplasm but primarily body-cell cytoplasm and male and egg nucleoplasm. Plastids and mitochondria for the proembryo were thus of paternal origin. Gamete structure and development, fertilization, and the ultrastructural mechanism for cytoplasmic inheritance in Agathis are compared to that in other conifer families.

Sperm-egg interactions in an Australian dasyurid marsupial with official reference to changes in acrosomal morphology.

The morphology of the acrosome of spermatozoa from an Australian dasyurid marsupial during in vivo fertilisation, as seen with the transmission electron microscope, is described. In some spermatozoa close to the outer zona surface with largely intact acrosomes, electron-dense struts between the inner and outer acrosomal membranes could be seen; in addition fusion between the outer acrosomal and overlying plasma membrane was sometimes evident. The zona matrix close to the acrosomal region of spermatozoa with heads partly embedded within the zona pellucida was less electron-dense and more filamentous than elsewhere; perhaps indicative of local lytic activity. Nevertheless some of these spermatozoa at least had partly intact acrosomes with localised regions of electron-dense bridges between the two acrosomal membranes. Spermatozoa with condensed chromatin were also observed within the egg cytoplasm some of which had membranes, vacuoles or cisternae close to the dorsal nuclear surface which could, in part, be acrosomal in origin. These observations lend some support to the recent view, based on findings from an American species, that acrosomal changes of spermatozoa of some marsupials at the time of fertilisation may be somewhat similar to those of eutherian mammals in spite of the considerable differences in gamete structure and design. How generally applicable these findings are to all marsupials remains, however, to be determined.

Flagellar apparatus of male gametes and other aspects of gamete and zygote ultrastructure in Prasiola and Rosenvingiella (Chlorophyta, Prasiolales) from British Columbia

We examined gametes, syngamy, and zygote formation in Prasiola meridionalis Setchell & Gardner and Rosenvingiella constricta (S. & G.) Silva with the transmission electron microscope. We compare the structures we observed with those of the Atlantic species P. stipitata Suhr and describe some previously unreported features. The sperm possessed a number of unusual structural elements in the flagellar apparatus and elsewhere, in particular a 9 + 1 microtubule configuration in the flagellar axoneme. The flagellar apparatus exhibited 180° rotational symmetry and counterclockwise absolute orientation of major components. At syngamy, the flagellar apparatus changed little in composition and arrangement, suggesting that it has a minimal, if any, function in syngamy or the planozygote. Karyogamy occurred within a few hours of plasmogamy, after settlement of the planozygote and concurrently with wall formation. The three species, P. meridionalis, P. stipitata, and R. constricta, are very similar in gamete structure, which indicates that the genera Prasiola and Rosenvingiella are close relatives. The flagellar apparatus features provide evidence supporting recognition of the order Prasiolales, which may be assigned to either the class Ulvophyceae or the class Pleurastrophyceae.

Mammalian fertilization as seen with the scanning electron microscope.

For several years we have been looking at mammalian gametes and their interactions with the scanning electron microscope (SEM). Examining the images produced by the SEM has given us a three-dimensional view of sperm, eggs, and egg investments. We are particularly impressed with the structural variation among gametes of different mammalian species. In this short report we examine the structure of mammalian spermatozoa, eggs, zonae pellucidae, and cumuli. Our observations and those of others have led us to believe that variation in gamete structure and function may have evolved as a mechanism for reproductive isolation of mammalian species.

Effets de faibles abaissements de température sur la différenciation de l'oosphère et sur les processus de fécondation chez le Marsilea vestita (Ptéridophytes)

Male and female gametes of Marsilea vestita were subjected to weak cooling periods (24° C/16° C or 24° C/12° C) of 1–4 h during the ultimate stage of gametogenesis. Effects of these suboptimal temperatures were observed on the organization of the oosphere on fertilization, and further development of the embryos. The changes observed varied with cold intensity and were proportional to the exposure time. The last steps of archegonogenesis were delayed (16° C) or even totally inhibited (12° C). The female gamete structure generally exhibited the following changes: the fertilization cone was enlarged, the cytoplasm more or less vacuolated, and organelles redistributed towards peripheral regions. Furthermore, the presence of chromatic fragments within the cytoplasm (12° C) suggests that the last division of female gametogenesis was strongly affected. In these gametes, fertilization was always reduced. When it occurred, the treatment considerably slowed down the different stages, allowing a better understanding of the male nucleus reactions during its migration. The percentage of embryos able to grow decreased proportionally to the length of cold exposure (16° C). After exposure of the gametes to 12° C, most embryos did not survive.

The effect of positive assortative mating at one locus on a second linked locus

Considerations proceed from a model of positive assortative mating based on genotype at one locus, with an arbitrary number of alleles, assuming no selection, mutation, or migration, hypothetically infinite population size, and discrete non-overlapping generations. From these conditions, inferences are made about the genotypic structure at a linked locus, as well as about the corresponding 2-locus gametic structure.The following main results are presented: in the course of the generations, the genotypic structure at the second locus and the 2-locus gametic structure always tend to a limit responsive to the initial conditions concerning the joint genotypic structure at the two loci and the degree of assortativity and linkage. A complete, analytical representation of the limits is given. In particular, if assortative mating is only partial and at the same time linkage is not complete, a population is not able to maintain a permanent deviation of the gametic structure from linkage equilibrium, and thus the genotypic structure at the second locus tends to Hardy-Weinberg proportions. On the other hand, if initial linkage disequilibrium is combined with partial assortative mating and complete linkage (or with complete assortative mating and unlinked loci) the population maintains this disequilibrium and thus the genotypic structure at the second locus need not tend to Hardy-Weinberg proportions. It turns out that the conditions not only of complete linkage, but also of unlinked loci together with complete assortativity, imply no change in gametic structure from the initial structure.In order to demonstrate the influence of several parameters on the speed of convergence to and the magnitude of the respective limits, several graphs are included.

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). II. GAMETES

Transmission electron microscopic examination of Cephaleuros virescens Kunze growing on leaves of Camellia sp. indicates that gametes are similar to those of Trentepohlia aurea. The gametes bear two, smooth isokont “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally. Each basal body is associated with a separate multilayered structure and component microtubular spline. The latter extends posteriorly beneath the plasmalemma. A nucleus, mitochondria, chloroplasts, and cytoplasmic haematochrome droplets are present. Pyrenoids and eyespots are absent. The subcellular components of C. virescens gametes are comparable to those found in gametes of T. aurea; however, the arrangement of basal bodies and multilayered structures differs slightly from that in T. aurea. Comparison of the fine structure of gametes from Cephaleuros, Phycopeltis, and Trentepohlia clearly indicates that the (1) mode of flagellar insertion, (2) morphology, number, and arrangement of multilayered structures, and (3) keeled flagella are common to these three genera and, thus far, unique among the green algae. Although flagellar insertion is apical, it is not bilaterally symmetrical (sensu stricto), nor is it asymmetrical (cf. Chara and Nitella sperms). The arrangement may be termed “reversed bilateral symmetry” and standardization of the terminology is recommended.

Ultrastructure of Cephaleuros virescens (Chroolepidaceae; Chlorophyta). II. Gametes

Transmission electron microscopic examination of Cephaleuros virescens Kunze growing on leaves of Camellia sp. indicates that gametes are similar to those of Trentepohlia aurea. The gametes bear two, smooth isokont “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally. Each basal body is associated with a separate multilayered structure and component microtubular spline. The latter extends posteriorly beneath the plasmalemma. A nucleus, mitochondria, chloroplasts, and cytoplasmic haematochrome droplets are present. Pyrenoids and eyespots are absent. The subcellular components of C. virescens gametes are comparable to those found in gametes of T. aurea; however, the arrangement of basal bodies and multilayered structures differs slightly from that in T. aurea. Comparison of the fine structure of gametes from Cephaleuros, Phycopeltis, and Trentepohlia clearly indicates that the (1) mode of flagellar insertion, (2) morphology, number, and arrangement of multilayered structures, and (3) keeled flagella are common to these three genera and, thus far, unique among the green algae. Although flagellar insertion is apical, it is not bilaterally symmetrical (sensu stricto), nor is it asymmetrical (cf. Chara and Nitella sperms). The arrangement may be termed “reversed bilateral symmetry” and standardization of the terminology is recommended.

Gametogenesis and gamete structure ofEnteromorpha intestinalis(L.) Link

The process of gametogenesis and gamete structure have been studied using scanning and transmission electron microscopy. Rounding off of the protoplast is followed by three mitotic divisions of the nucleus and cytokinesis to give eight gametes in each gametangium. Changes in wall structure of the gametangium and loosening of wall microfibrils takes place at the site of the future exit pore where the outer cell wall is stretched to form a characteristic “papilla”. Anisogametes are shed, each with two smooth flagella, a single nucleus, a very large chloroplast with a conspicuous pyrenoid and an eyespot composed of one layer of osmiophilic granules.

Fine structure of gametes of Nereis limbata (Annelida) before and after interaction.

AbstractThe acrosome of the Nereis limbata spermatozoon is a vesicular body which is shaped in the form of a double‐walled hollow cone. As such it encloses an axial chamber housin the anterior part of a rod‐like structure which, posteriorly, fits into a deep invagination in the nucleus. When the acrosome undergoes reaction preparatory to and during penetration of the egg envelope, it opens anteriorly, discharging its contents, and the axial chamber, together with its contained rod, is expanded and portruded as the acrosome filament.The chorion of the egg is about 0.7 μ thick, and is traversed completely by microvilli which project at intervals. Numerous broad canals extend about three‐quarters through the chorion. It is by one of these canals that the acrosome filament passes in the initial stages of sperm penetration.The cortex of the egg has a wide zone of densely packed alveoli which contain moderately electron‐dense material, the jelly precursor. Cortical reaction to sperm entry involves fusion between adjacent alveoli and opening up of alveoli onto the cytoplasmic surface of the egg. Released jelly precursor, evidently becoming hydrated, flows into the perivitelline space and thence through the pores in the chorion that accommodate the microvilli (flowing around the microvilli which persist), so as to form a thick layer about the egg.

Studies on the Morphology and Behaviour of the Reproductive Cells of <i>Chaetomorpha Okamurai</i> Ueda

Some new knowledges concerned with reproduction and reproductive cells of a freshwater alga, Chaetonaarpha Okamurai Ueda are summarized as follows:1) The structure of fertile filaments of the present alga is described.2) Developmental processes of liberation pore formation are observed. Inner layer of cellwall firstly opens and later opens outer layer. Shedding out processes of swarmers are also described.3) Shapes and structure of gametes and zoospores are described and their dimensions are measured too.4) Sexual fusion takes its place not only among those gametes which are ejected from different filaments as commonly encountered as in most of algae, but also among those gametes ejected from a single filament. Moreoverr sometimes even among those gametes which are produced in a same game-tangium of a single filament sexual fusions are observed.5) Several types concerned with gamete fusions are enumerated: i. Anterior with anterior, ii. Anterior with ventral, iii. Posterior with pos-terior, iv. Posterior with anterior and v. Random-touching.6) Zygotes always become planozygotes and their motility never be weakened for a comparatively long time.7) In early autumn gametes often stand still and grow to become sporings parthenogenetically.8) The present alga is perennial and her method of reproduction is mainly by means of gamete formation through a year only excepting for by means of zoospores in early May and in early September.9) Phototaxis of swarmers of the present alga is differently characterized by each swarmer, namely positive by gametes and negative by zoospores, planozygotes and parthenogametes.10) Zygotes, zoospores and parthenogametes were cultured. The germination type of these three sorts of reproductive cells all belong to Inoh's “Immediate Filamentous Type” After 54 days' culture of zygotes and zoospores, their sporings grew to reach up to 665μ in length being composed of two to five much elongated cells.