certain amount of unused sporoplasm left over in the centre of the
spore, constituting the sporal residuum. It is important to note that
in all known Gregarines, with one exception, the number of sporozoites
in the spore is eight; the exception is Selenidium, in many
ways far from typical, where the number is half, viz. four.
 |
|
Fig. 15.—Ripe Cyst of Gregarina blattarum, partially emptied. (From Lankester.) a, Channels leading to the sporoducts; b, Mass of spores still left in the cyst; c, Endocyst; d, The everted sporoducts; e, Gelatinous ectocyst. |
Hitherto a variation from the general mode of spore-formation has been considered to occur in certain Crustacean Gregarines, the Aggregatidae and the Porosporidae. The spores of these forms have been regarded as gymnospores (naked), lacking the enveloping membranes (sporocyst) of the ordinary spores, and the sporozoites, consequently, as developed freely in the cyst. In the case of the first-named parasites, however, what was taken for sporogony has been proved to be really schizogony, and on other grounds these forms are, in the present writer’s opinion, preferably associated with the Coccidia (q.v.). With regard to the Porosporidae, also, it is quite likely that the gymnosporous cysts considered to belong to the Gregarine Porospora (as known in the trophic condition) have really no connexion with it, but represent the schizogonous generation of some other form, similar to Aggregata; in which case the true spores of Porospora have yet to be identified.
In the intestine of a fresh host the cysts rupture and the spores are liberated. This is usually largely brought about by the swelling of the residual protoplasm. Sometimes (e.g. Gregarina) long tubular outgrowths, known as sporoducts (fig. 15), are developed from the residual protoplasm, for the passage of the spores to the exterior.
The Gregarines are extremely numerous, and include several families, characterized, for the most part, by the form of the spores (fig. 16). The specialized Schizogregarinae are usually separated off from the rest as a distinct sub-order.Classification.
Sub-order I.—Schizogregarinae.
Forms in which schizogonic reproduction is of general occurrence during the extra-cellular, trophic phase. Three genera, Ophryocystis, Schizocystis and Eleutheroschizon, different peculiarities of which have been referred to above. Mostly parasitic in the intestine or Malpighian tubules of insects. (In this type of parasite, as exemplified by Ophryocystis, the body was formerly wrongly considered as amoeboid, and hence this genus was placed in a special order, the Amoebosporidia.)
 | ||
| From Wasielewski, after Léger. | ||
| Fig. 16.—Spores of various Gregarines. | ||
| a, Eirmocystis, Sphaerocystis, &c. | f, Stylorhynchidae (type of). | |
| b, Echinomera, Pterocephalus, &c. | g, Menosporidae. | |
| c, Gregarina, &c. | h, Gonospora terebellae. | |
| d, Beloides. | i, Ceratospora. | |
| e, Ancyrophora. | k, Urospora synaptae. | |
Sub-order II.—Eugregarinae.
Schizogony very exceptional, only occurring during the intracellular phase, if at all. Gregarines fall naturally into two tribes, described as cephalont and septate, or as acephalont and aseptate (haplocytic), respectively. In strictness, however, as already mentioned, these two sets of terms do not agree absolutely, and whichever set is adopted, the other must be taken into account in estimating the proper position of certain parasites. Here the cephalont or acephalont condition is regarded as the more primary and fundamental.
Tribe A.—Cephalina (practically equivalent to Septata).
Save exceptionally, the body possesses an epimerite, at any rate during the early stages of growth, and is typically septate. Mostly intestinal parasites of Arthropods.
The chief families, with representative genera, are as follows: Porosporidae, with Porospora gigantea, at present thought to be gymnosporous; Gregarinidae (Clepsydrinidae), with Gregarina, Clepsydrina, Eirmocystis, Hyalospora, Cmenidospora, Stenophora; Didymophyidae, with Didymophyes; Dactylophoridae, with Dactylophorus, Pterocephalus, Echinomera, Rhopalonia; Actinocephalidae with Actinocephalus, Pyxinia, Coleorhynchus, Stephanophora, Legeria, Stictospora, Pileocephalus, Sciadophora; Acanthosporidae with Acanthospora, Corycella, Cometoides; Menosporidae with Menospora, Hoplorhynchus; Stylorhynchidae, with Stylorhynchus, Lophocephalus; Doliocystidae with Doliocystis; and Taeniocystidae, with Taeniocystis. The curious genus Selenidium is somewhat apart.
Tribe B.—Acephalina (practically equivalent to Aseptata, Haplocyta).
The body never possesses an epimerite and is non-septate. Chiefly coelomic parasites of “worms,” Holothurians and insects.
The Aseptata have not been so completely arranged in families as the Septata. Léger has distinguished two well-marked ones, but the remaining genera still want classifying more in detail. Fam. Gonosporidae, with Gonospora, Diplodina; and Urosporidae, with Urosopora, Cystobia, Lithocystis, Ceratospora; the genera Monocystis, Diplocystis Lankesteria and Zygocystis probably constitute another; Pterospora and, again, Syncystis are distinct; lastly, certain forms, e.g. Zygosoma, Anchora (Anchorina), are incompletely known.
There remains for mention the remarkable parasite, recently described by J. Nusbaum (24) under the appropriate name of Schaudinnella henleae, which inhabits the intestine of Henlea leptodera. Briefly enumerated, the principal features in the life-cycle are as follows. The young trophozoites (aseptate) are attached to the intestinal cells, but practically entirely extracellular. Association is very primitive in character and indiscriminate; it takes place indifferently between individuals which will give rise to gametes of the same or opposite sex. Often it is only temporary; at other times it is multiple, several adults becoming more or less enclosed in a gelatinous investment. Nevertheless, in no case does true encystment occur, the sex-cells being developed practically free. The female gametes are large and egg-like; the males, minute and sickle-like, but with no flagellum and apparently non-motile. While many of the zygotes (“amphionts”) resulting from copulation pass out to the exterior, to infect a new host, others, possessing a more delicate investing-membrane, penetrate in between the intestinal cells, producing a further infection (auto-infection). Numerous sporozoites are formed in each zygote. It will be seen that Schaudinnella is a practically unique form. While, on the one hand, it recalls the Gregarines in many ways, on the other hand it differs widely from them in several characteristic features, being primitive in some respects, but highly specialized in others, so that it cannot be properly included in the order. Schaudinnella rather represents a primitive Ectosporan parasite, which has proceeded upon a line of its own, intermediate between the Gregarines and Coccidia.
Bibliography.—Among the important papers relating to Gregarines are the following: 1. A. Berndt, “Beitrag zur Kenntnis der . . . Gregarinen,” Arch. Protistenk. I, p. 375, 3 pls. (1902); 2. L. Brasil, “Recherches sur la reproduction des Grégarines monocystidées,” Arch. zool. exp. (4) 3, p. 17, pl. 2 (1905), and op. cit. 4, p. 69, 2 pls. (1905); 3. L. Brazil, “Eleutheroschizon duboscqi, parasite nouveau, &c.,” op. cit. (N. et R.) (4), p. xvii., 5 figs. (1906); 4. M. Caullery and F. Mesnil, “Sur une Grégarine . . . présentant . . . une phase de multiplication asporulée,” C.R. Ac. Sci. 126, p. 262 (1898); 5. M. Caullery and F. Mesnil, “Le Parasitisme intracellulaire des Grégarines,” op. cit. 132, p. 220 (1901); 6. M. Caullery and F. Mesnil, “Sur une mode particulière de division nucléaire chez les Grégarines,” Arch. anat. microsc. 3, p. 146, 1 pl. (1900); 7. M. Caullery and F. Mesnil, “Sur quelques parasites internes des Annélides,” Misc. biol. (Trav. Stat. Wimereux), 9, p. 80, 1 pl. (1899); 7a. J. Cecconi, “Sur l’Anchorina sagittata, &c.,” Arch. Protistenk. 6, p. 230, 2 pls. (1905); 8. H. Crawley, “Progressive Movement of Gregarines,” P. Ac. Philad. 54, p. 4, 2 pls. (1902), also op. cit. 57, p. 89 (1905); 9. H. Crawley, “List of the Polycystid Gregarines of the U.S.,” op. cit. 55, pp. 41, 632, 4 pls. (1903); 10. L. Cuénot, “Recherches sur l’évolution et la conjugaison des Grégarines,” Arch. biol. 17, p. 581, 4 pls. (1901); 11. A. Laveran and F. Mesnil, “Sur quelques particularités de l’évolution d’une Grégarine et la réaction de la cellule-hôte,” C.R. Soc. Biol. 52, p. 554, 9 figs. (1900); 12. L. Léger, “Recherches sur les Grégarines,” Tabl. zool. 3, p. i., 22 pls. (1892); 13. L. Léger, “Contribution à la connaissance des Sporozoaires, &c.,” Bull. Sci. France, 30, p. 240, 3 pls. (1897); 14. L. Léger, “Sur un nouveau Sporozoaire (Schizocystis), &c.,” C.R. Ac. Sci. 131, p. 722 (1900); 15. L. Léger, “La Reproduction sexuée chez les Ophryocystis,” t. c. p. 761 (1900); 16. L. Léger, “Sur une nouvelle Grégarine (Aggregata coelomica,), &c.” op. cit. 132, p. 1343 (1901); 17. L. Léger, “La Reproduction sexuée chez les Stylorhynchus,” Arch. Protistenk. 3, p. 304, 2 pls. (1904); 18. L. Léger, “Etude sur Taeniocystis mira (Léger), &c.,” op. cit. 7, p. 307, 2 pls. (1906); 19. L. Léger and O. Duboscq, “La Reproduction sexuée chez Pterocephalus,” Arch. zool. exp. (N. et R.) (4) 1, p. 141, 11 figs. (1903); 20. L. Léger and O. Duboscq, “Aggregata vagans, n. sp., &c.” t. c. p. 147, 6 figs. (1903); 21. L. Léger and O. Duboscq, “Les Grégarines et l’épithélium intestinal, &c.,” Arch. parasitol. 6, p. 377, 4 pls. (1902); 22. L. Léger and O. Duboscq, “Nouvelles Recherches sur
