Quite recently much additional light has been thrown upon our knowledge of these parasites, including a new one, E. jacquemeti. Moroff (1906) has shown that not one but many megagametes are formed, and fertilized by the microgametes. For this reason he regards them as Gregarines rather than Coccidia. Further, Léger and Duboscq (1906) have found that the characteristic coelomic parasites (Aggregata) of Crustacea, generally regarded as gymnosporous Gregarines (i.e. Gregarines in which the sporozoites are naked) constitute in reality nothing more or less than a schizogonous generation of these Cephalopodan parasites, which have thus an alternation of true hosts. The ripe sporocysts from the Cephalopod are eaten by a particular crab (e.g. Portunus or Inachus, according to the parasite), the sporozoites are liberated and traverse the mucous membrane of the intestine, coming to rest in the surrounding lymphatic layer. Here a large “cyst” is formed, projecting into the body-cavity, the contents of which give rise to a great number of merozoites. On the crab being devoured by the right species of Cephalopod, the merozoites doubtless give rise to the sexual generation again.
As the name Aggregata is much the older, and as, moreover, there is no longer any reason to retain that of Eucoccidium, these parasites must in future receive the former generic appellation. With regard to the various specific names, however, they remain quite unsettled until the life-history is properly worked out in different cases (see also [Gregarines]).
It seems to the writer a much more open question than Moroff and Léger and Duboscq apparently suppose, whether these parasites are to be relegated to the Gregarines. For undoubtedly they have many Coccidian features, and on the other hand they differ in many ways from Gregarines. The chief feature of agreement with the latter order is the possession of many female gametes. As already said, there can be little doubt that this was the condition in the Coccidian ancestor, and it is by no means impossible that one or two forms existing at the present day remain primitive in that respect. On the other hand, the advanced character of the parasitism (the parasites remaining intracellular up to and including gamete-formation); the entire lack of the characteristic feature of association; the schizogony, which is only a very rare occurrence in Gregarines, and which, in the present case, strongly suggests the process in Caryotropha and Klossiella; and, last but not least, the varying number of the sporozoites (3 in one form, 10-15 in others), which is very different from the almost constant number (8) in Gregarines, are all characters in which these forms agree with Coccidia and not with Gregarines. Having regard to these points, the writer is inclined, for the present, to consider Aggregata as an offshoot rather from the Coccidian than from the Gregarine branch of the Ectosporan tree.
Bibliography.—The following are some of the important papers dealing with the order:—G. Bonnet-Eymard, “Sur l’Évolution de l’Eimeria nova, Schneider,” C.R. Soc. Biol. 52, p. 659, 1900; L. Brasil, “Sur une Coccidie nouvelle, &c.,” C.R.Ac. Sci. 139, p. 645, 1904; L. Cuénot, “Légerella testiculi n. sp., &c.,” Arch. Zool. exp. (N. et R.), (3) 10, p. 49, 6 figs., 1902; M. Jacquemet, “Sur la systématique des Coccidies des Céphalopodes,” Arch. Protistenk. 2 p., 190, 1903; A. Labbé, “Recherches zoologiques, cytologiques et biologiques sur les Coccidies,” Arch. zool. exp. (3), 4, p. 517, 3 pls., 1897; A. Laveran, “Sur les modes de réproduction d’Isospora lacazei,” C.R. Soc. Biol. 50, p. 1139, 1898; A. Laveran and F. Mesnil, “Sur deux Coccidies intestinales de la Rana esculenta,” op. cit. 54, p. 857, 9 figs., 1902; A. Laveran and F. Mesnil, “Sur la Coccidie trouvée dans le rein de la Rana esculenta, &c.,” C.R.Ac. Sci. 135, p. 82, 10 figs., 1902; A. Laveran and F. Mesnil, “Sur quelques Protozoaires parasites d’une tortue, &c.” t. c. p. 609, 14 figs., 1902; L. Léger, “Sur une nouvelle Coccidie à microgamètes ciliés,” op. cit., 127, p. 418, 1898; L. Léger, “Sur la morphologie et le développement des microgamètes des Coccidies,” Arch. zool. exp. (N. et R.) (3), 6, 1898; L. Léger, “Essai sur la classification des Coccidies, &c.,” Ann. Mus. Nat. Hist., Marseille (2), Bull. i. p. 71, 4 pls., 1898; L. Léger “Sur la présence d’une Coccidie coelomique chez Olocrates, &c.,” Arch. zool. exp. (N. et R.) (3), 8, p. i., 1900; L. Léger, “Sur le genre Eimeria et la classification des Coccidies,” C.R. Soc. Biol. 52, p. 575, 1900; L. Léger and O. Duboscq, “Recherches sur les Myriapodes de Corse et leurs parasites,” Arch. zool. exp. (4), 1, p. 307, 24 figs., 1903; L. Léger and O. Duboscq, “Sur l’évolution des Grégarines gymnosporées des Crustacés,” C.R.Ac. Sci. 142, p. 1225, 1906; L. Léger and O. Duboscq, “L’Évolution d’une Aggregata de la seiche chez le Portunus depurator,” C.R. Soc. Biol. 6o, p. 1001, 1906; M. Lühe, “Über Geltung und Bedeutung der Gattungsnamen Eimeria und Coccidium,” C.B. Bakter (1) 31 Orig, p. 771, 1902; C.B. Bakter, “Die Coccidien-Literatur der letzten vier Jahre,” Zool. Centrlbl. 10, 45 pp., 1903; F. Mesnil, “Sur la conservation du nom générique Eimeria, &c.,” C.R. Soc. Biol. 52, p. 603, 1900; F. Mesnil, “Les Travaux récents sur les Coccidies,” Bull. Inst. Pasteur, i. pp. 473, 505, 1903; R. Metzner, “Untersuchungen an Coccidium cuniculi,” Arch. Protistenk. 2, p. 13, pl. ii. 1903; G. Moussu and G. Marotel, “La Coccidiose du mouton et son parasite,” Arch. Parasitol. 6, p. 82, 10 figs., 1902; T. Moroff, “Sur l’évolution des prétendues Coccidies des Céphalopodes,” C.R.Ac. Sci. 142, p. 652, 1906; C. Perez, “Le Cycle évolutif de l’Adelea mesnili, &c.,” Arch. Protistenk. 2, p. 1, pl. 1, 1903; F. Schaudinn, “Untersuchungen über den Generationswechsel bei Coccidien,” Zool. Jahrbücher (Anat.) 13, p. 197, 4 pls., 1900; F. Schaudinn, “Studien über krankheitserregende Protozoen—I. Cyclospora caryolytica, &c.,” Arb. kais. Gesundh.-amte, 18, p. 378, 2 pls., 1902; M. Siedlecki, “Réproduction sexuée ... chez ... Coccidium proprium,” C.R. Soc. Biol. 50, p. 664, figs., 1898; M. Siedlecki, “Étude cytologique ... de la Coccidie de la seiche, &c.,” Ann. Inst. Pasteur, 12, p. 799, 3 pls., 1898; M. Siedlecki, “Étude cytologique ... de Adelea ovata,” op. cit. 13, p. 169, 3 pls., 1899; M. Siedlecki, “Cycle évolutif de la Caryotropha mesnilii, &c.,” Bull. Ac. Cracovie, p. 561, 5 figs., 1902; T. Smith and H. P. Johnson, “On a Coccidian (Klossiella muris, gen. et spec. nov.), &c.,” J. exp. Med. 6, p. 303, 3 pls., 1902; H.M. Woodcock, “Notes on Sporozoa, I. On Klossiella muris, &c.,” Q.J. micr. Sci. 48, p. 153, 2 figs., 1904.
(H. M. Wo.)
[1] A curious organism, parasitic in a gregarine, has lately been described by Dogiel as a coccidian, and termed Hyalosphaera.
[2] It is important to note that in schizogony there is never any cyst or cyst-membrane formed around the parasite.
[3] The merozoites are frequently arranged like the staves of a barrel—whence the term barillet, which is frequently used.
[4] In Cyclospora, Schaudinn (1902) has noted certain abnormal cases of the persistence and further multiplication of the “reduction-nuclei” of the female element (i.e. the nuclear portions given off during maturation), followed by multiple fertilization. This occurrence points strongly to the conclusion that there were originally many female gametes (cf. also the sporoblasts of Gregarines).