Phaenocystes the polar-capsules are visible in the fresh condition, but not in the Cryptocystes. The polar-capsule is an organella which recalls the nematocyst of a Hydrozoan, containing a spirally-coiled filament, often of great length, which is shot out on the application of a suitable stimulus. Normally, as was ingeniously shown by Thélohan (43), the digestive juices of the fresh host serve this purpose, but various artificial means may suffice. The function of the everted filament is probably to secure the attachment of the spore to the epithelium of the new host. In the Phaenocystes, in connexion with each polar-capsule, a small nuclear body can be generally made out; these two little nuclei are those of the two “capsulogenous” areas of the protoplasm of the pansporoblast, which formed the capsules. The sporoplasm, representing the sporozoite, is always single. Nevertheless, in the Phaenocystes it is invariably binuclear; and, in the Microsporidia, the nucleus, at first single, gives rise later to four nuclei, two of which are regarded by Stempell (42) as corresponding to those of two polar-capsules (of which only one is developed in the spore), the remaining two representing germ-nuclei. Hence it is possible that the Myxosporidian sporoplasm really consists of two, incompletely-divided (sister) germs. Moreover, it is supposed by some that these two nuclei fuse together later, this act representing a sexual conjugation; since the earliest known phases of young trophozoites (amoebulae) have been described as uninuclear.
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| From Lankester’s Treatise on Zoology, vol. Protozoa, after Thélohan. | |
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Fig. 4.—Stages in spore-formation. All the figures are from Myxobolus ellipsoides, except a and f, which are from M. pfeifferi. a, Differentiation of the pansporoblast (p.sp). b, Pansporoblast with two nuclei. c and d, Pansporoblasts with six and ten nuclei respectively; in d, four of the nuclei are degenerating. e, Pansporoblast segmented into two definitive sporoblasts, each with three nuclei. In the next four figures the definitive sporoblast, or the spore produced from it, is alone figured. f, Definitive sporoblast segmented into three masses, the capsulogenous cells (c.g.c) and the sporoplasm (sp.p), within an envelope, the spore membrane (sp.m). g, More advanced stage. h, Spore completely developed, with two polar capsules and sporoplasm containing an iodinophilous vacuole. i, Abnormal spore containing six polar capsules. | |
| n, Nuclei. | sp.bl, Definitive sporoblast. |
| r.n, Residuary nuclei. | vac, Vacuole. |
| r.p.c, Rudiment of p.c, polar capsule. | n.p.c, Nuclei of polar capsules. |
| iod.vac, Iodinophilous vacuole. | n.sp, Nuclei of sporoplasm. |
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| From Woodcock, Proc. and Trans. of the Liverpool Biological Society, 1904. |
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Fig. 5.—Part of the periphery of a cyst of Glugea stephani, in the intestinal wall of the plaice, showing sporoblast and spore-formation. ect, Ectorind. end, Endoplasm. endoth, Fold of the mucous membrane, normal in character. p.sp.bl, Various stages in the development of the pansporoblasts. sp, Ripe spores, filling the greater part of the cyst. n, Large (vegetative) nuclei. |
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From Lankester’s Treatise on |
Fig. 6.—Formation of buds by multiple plasmotomy in Myxidium lieberkühnii, Bütschli (par. Esox and Lota) after Cohn. |
In addition to spore-formation, two or three modes of endogenous reproduction, serving for auto-infection, have been made known. One, termed by Doflein plasmotomy, consists either in the division of the (multinucleate) trophozoite into two, by more or less equal fission (simple plasmotomy), or in the budding-off, from the parent trophozoite, of several portions (example: Myxidium lieberkühnii, fig. 6). A variety of this method has been described by Stempell (40) in the case of the young trophozoites (meronts) of Thelohania mülleri, which may divide into two while still uninuclear; and by rapid successive divisions chains of meronts may be formed, the different individuals being incompletely separated. Another method, which is probably chiefly responsible for the rapid spread of tissue-parasites and cell-parasites (such as Myxobolidae and Glugeidae) through their host’s tissue in the condition of diffuse infiltration, consists in multiple nuclear division, and the liberation of amoebulae while the parasite is yet quite young and possesses only few nuclei. As Woodcock has pointed out in considering the case of Glugea stephani, it is very probable that this “multiplicative reproduction,” in diffuse infiltration, is to be looked upon as a separation of the pansporoblast-rudiments as daughter-individuals; i.e. that the pansporoblasts are, in certain circumstances, capable of independent existence as little sporonts. A further stage in this direction of evolution is seen, according to Stempell, in Thelohania, Pleistophora and other types where the whole individual becomes one reproductive organella; such forms are to be considered as examples of a phylogenetic individualization of the pansporoblasts, which now exist as solitary sporonts. An extreme case of this “reduction of the individual” is found, apparently in the genus Nosema, as lately characterized by Perez (34), where vast numbers of minute entirely independent sporonts (pansporoblasts) are produced, each of which gives rise to only a single spore.
The Myxosporidia are divided into two suborders, the Phaenocystes and the Cryptocystes. Some authors have of late years separated these two divisions and raised each to the rank of a distinct order, considering that they are not more closely related to each other than to other Endosporan orders. We think this is a mistake; and it is very interesting to find that Léger and Hesse (1908) have described (29a) a new genus of Phaenocystes, Coccomyxa, which represents a type intermediate between these two suborders, and shows that they are closely connected.
Suborder 1: Phaenocystes, Gurley. Spores relatively large, with generally two or four polar-capsules, visible in the fresh condition. There are nearly always two spores formed Classification. in each pansporoblast.
Section (a): Disporea. Only two spores (i.e. one pansporoblast) produced in each individual trophozoite. The greatest length of the spore is at right angles to the plane of the suture.
One family, Ceratomyxidae, including two genera, Ceratomyxa (fig. 3, B) and Leptotheca, typically “free” parasites, mostly from the gall bladders of fishes. The valves of the spore in the former genus are prolonged into hollow cones. The type-species of this genus is C. sphaerulosa, from Mustelus and Galeus; that of Leptotheca is L. agilis, from Trygon.
Section (b): Polysporea. More than two spores, generally very many, are produced typically by each individual trophozoite. The greatest length of the spore is usually in the sutural plane.
Family, Myxidiidae. Spores with two polar-capsules, and without an iodinophilous vacuole in the sporoplasm. Mostly “free”
