SPOROZOA.] 0. Anterior end of the same more highly magnified, a, protomerite ; 6, layer of circular nbrillso lying below the cuticle ; c, cortical substance of the deutomerite; d, medullary substance of the deutomerite. 10. Two spores of Gregarina tjigantea (after Biitschli), showing the very thick coat of the spore. 11-15. Stages in the development of Gregarina gir/antea-.ll, recently escaped from the spore-coat, no nucleus ; 12, still no nucleus, one vibratile and one motionless process ; 13, the two processes have divided ; one here drawn has developed a nucleus ; 14, further growth ; 15, the deutomerite commences to develop. 16. Cysts of Gregarina gigantea, from the rectum of the Lobster. The double contents are believed by Ed. Van Beneden to be due not to conjugation previous to encystment but to subsequent fission. 17, 18. Gregarina longicol/is, Stein, from the intestine of Blaps mortisaga : 17, cephalont phase, with a long proboscis-like epimerite a, attached to the protomerite b ; 18, sporont phase, the epimerite having been cast preliminarily to syzygy and encystment. 19. Gregarina Manieri, Aim. Schneider, from the intestine of Timarcha knebricoxa, to show the network of anastomosing fibres beneath the cuticle, similar to the annular fibriHae of G. gigantea shown in 9. 20. Gregarina (Hoplorhynchus) obliijacanthus, Stein, from the intestine of the larva of Agrion. Cephalont with spine-crowned epimerite a. 21. Spores of Gregarina oligacanthus. 22, 23. Grega rina (Hoplorht/nclius) Dtijardini, Aim. Schneider, from the intestine of Lithobius forficatus : 22, specimen with epimerite a, therefore a " cepha lont"; 23, specimen losing its epimerite by rupture and becoming a " sporont." ORDER 2. OLIGOSPOREA, Aim. Sclin. diameters. The cyst-content develops itself into a definite and constant but small number of spores. Genus unicnm. Coccidium, Leuck. (in intestinal epithelium and liver of Mammals, and some Invertebrates, Figs. XVII. 24 to 31). ORDER 3. POLYSPOREA. Characters. The cyst-content develops itself into a great num ber of spores (sixty or more). Genus iinicum. Klossia, Aim. Sclin. Three species of Klossia are found in Mollusca viz., in Helix, in Cephalopods, and in Chiton. Schneider s genus, Adelea, from Lithobius, appears to belong here. Kloss (49) discovered the parasite of the renal cells of Helix hortcHsis represented in Fig. XVII. 18, 19, 20, 21, and 22; Schneider that of Cephalopods, Fig. XVII. 32, 33. In Chiton Dr Tovey has discovered a third species with very remarkable spores, which are here figured for the first time (Fig. XVII. 12). The Drepanidium Ranarum (Fig. XVII. 45, 46, 47), discovered by Lankester (50) in the Frog s blood, is probably the falciform young of a Coccidium parasitic in the Frog s kidney, and discovered there by Lieberkiihn (51). A spore of this Coccidium is shown in Fig. XVII. 48; whilst in 46 two Drepanidia which have penetrated a red-blood corpuscle of the Frog are represented. The Polypporoua Coccidiidea come very close to the Gregariniue genus Monocystis, from which they may be considered as being derived by an arrest of development. The spores and falciform young of the Coccidiidea are closely similar to those of Monocystis, and the young in both cases penetrate the tissue-cells of their host ; but in Monocystis this is only a temporary condition, and growth leads to the cessation of such "cell-parasitism." On the other hand, growth is arrested in the Coccidiidea, and the organism is permanently a cell-parasite. Since the parasitism is more developed in the case of a cell-para site than in the case of a parasite which wanders in the body cavity, it seems probable that the Coccidiidea have been derived from the Gregarinidea rather than that the reverse process has taken place. SUB-CLASS III. Myxosporidia, Biitschli. Characters. Sporozoa in which the euglena-phase is a large multiiiucleate amoeba-like organism (Fig. XVII. 34). The cysts are imperfectly known, but appear to be simple ; some attain a diameter of two lines. The spores are highly characteristic, having each a thick coat which is usually provided with a bifurcate process or may have thread capsules (like nematocysts) in its substance (Fig. XVII. 40, 41, 42, 43, 44). The spores contain a single nucleus, and are not known to produce falciform young, but in one case have been seen to liberate an amcebula. The further development is unknown. The Myxo sporidia are parasitic beneath the epidermis of the gills and fins, and in the gall-bladder and urinary bladder of Fishes, both freshwater and marine. Genera. Myxidium, Biitschli (Pike, Fig. XVII. 34); Afyzobolus, Biitschli (Cyprinoids) ; Lithocystis, Giard (the Lamellibranch Echino- cardium). The Myxosporidia are very imperfectly known. They present very close affinities to the Mycetozoa, and are to be regarded as a connecting link between the lower Gymnomyxa and the typical Sporozoa. Possibly their large multinucleate amoeba phase is a plasmodium formed by fusion of amcebulse set free from spores, though it is possible that the many nuclei are the result of a division of an original single nucleus, preparatory to sporulation. Their spores are more elaborate in structure than those of any other Protozoa, and are more nearly paralleled by those of some species of Monocystis than by those of Mycetozoa. The thread- capsules of the spores are identical in structure with those of Hydrozoa, and probably serve as organs of attachment, as do the furcate processes of the spore-case. It is not certain that a definite 855 cyst is always or ever formed, but as occurs rarely in some Gregari nidea, the spores may be formed in a non encysted amoeba form. Although pseudopodia, sometimes short and thread-like, have been observed in the amoeba phase, yet it is also stated that a distinction of cortical and medullary substance obtains. The " psorosperms " of J. Miiller are the spores of Myxosporidin. SUB-CLASS IV. Sarcocystidia, Biitschli. (This division is formed by Biitschli for the reception of Sarco- cystis, parasitic in the muscular iibres of Mammals, and of Amcebi- diuin, parasitic in Crustacea. Both are very insufficiently known, but have the form of tubular protoplasmic bodies in which numer ous ovoid spores are formed from which falciform young escape. ) Genera. Sarcocystis, Lankester ; Amcebidium, C ienkowski (52). Sarcocystis(Fig. XVII. 50, 51, S. Miescheri, Lank.), was first observed by Miescher in the striated muscle-fibres of the Mouse ; then by Rainey in a similar position in the Pig, and taken by him for the youngest stage in the development of the cysts of T&nia solium ; subsequently studied by Beale and others in connexion with the cattle-plague epidemic, and erroneously supposed to have a causal connexion with that disease. It is common in healthy butcher s meat. See Leuckart (47). Further remarks on the Sporozoa. The Sporozoa contrast strongly with the large classes of Gymnomyxa, the Heliozoa, Reticularia, and Radiolaria, as also with the C iliate and Tentaculi- ferous Corticata, by their abundant and rapidly recurrent forma tion of spores, and agree in this respect with some Proteomyxa, with Mycetozoa, and some Flagellata. Their spores are remark able for the firm, chitin-like spore-coat and its varied shapes, contrasting with the cellulose spherical spore-coat of Mycetozoa and with the naked spores of Radiolaria and Flagellata. The protoplasm of the more highly developed forms (Gregarini dea) in the euglenoid phase exhibits considerable differentiation. Externally a distinct cuticle may be present, marked by parallel rugfe (Monocystis serpulee) or by fine tubercles (Monocystis sipun- culi). A circlet of hooks may be formed by the cuticle at one end of the body. Below the cuticle is sometimes developed a layer of fibrils running transversely to the long axis of the body (Fig. XIX. 9 and 19), which have been regarded as contractile, but are probably cuticular. The cortical layer of protoplasm below these cuticular structures is dense and refringent and sometimes fibril- lated (Monocystis pcllucida, Fig. XVII. 15). It is the contractile- substance of the organism, and encloses the finely granular more liquid medullary substance. The granules of the latter have been shown by Biitschli (9) to give a starch-like reaction with iodim, &c. Probably the protoplasm in which they lie is finely reticulate or vacuolar, and when the granules are few it is actually seen to be so. No contractile vacuole is ever present. In Myxosporidia tin; medullary protoplasm is coloured yellow by h&matoidin derived from the blood of its host or by absorbed bile-pigment, and also contains small crystals. The nucleus of the Gregarinidea is a large clear capsule, with a few or no nucleolar granules. It has never been seen in a state of division, and it is not known what becomes of it during sporula tion, though sporulating Gregarinidea have been observed with many minute nuclei scattered in their protoplasm, presumably formed by a breaking up of the single nucleus. The habit of attaching themselves in pairs which is common in Gregarinidea is perhaps a reminiscence of a more extensive forma tion of aggregation plasmodia (compare Mycetozoa). The term "syzygium" is applied to such a conjunction of two Gregarinidea ; it is not accompanied by fusion of substance. The formation of cysts is not connected with this pairing, since the latter occurs in young individuals long before encystment. Also cysts are formed by single Gregarinidea, as is always the case in the non-motile Coccidiidea. The encystment always leads to the formation of spores, but in rare cases sporulation has been observed in unencysted Gregarini dea, and it occurs perhaps normally without true cyst-formation in the Myxosporidia. The cell-parasitism of the young Sporozoa, and their flagellula- like (falciform) young and active vibratile movement, are points indicating affinity with the lower Gymnomyxa, and especially with those Proteomyxa, such as Vampyrella and Plasmodiophora, which are cell-parasites. Indeed it is probable that we have in this fact of cell-parasitism, and especially of parasitism in animal cells, a basis for the theoretical association of several unicellular organisms. The Haplococcus of Zopf (regarded by him as a Mycetozoon) is parasitic in the muscular cells of the Pig, and is probably related to Sarcocystis. Recently Von Lendenfeld (53) has described in Australia an amoeba-like organism as parasitic in the skin of Sheep, which will probably be found to be either a Sporozoon or referable to those parasitic spore-producing Proteomyxa which are separated from Sporozoa only by their negative characters (see previous remarks on the negative characters of Proteomyxa).
The application of the name " Gregarines " has sometimes been