SPOEOZOA.] PROTOZOA 853 The Sporozoa are divided into four sub-classes, differing from one another according to the form and development attained by the euglena phase. We shall place the most highly developed first, not only because our knowledge about it is most complete, but because it is possible that one at least of the other sub-classes is derived by degeneration from it. SUB-CLASS I. Gregarinidea, Biitschli (9). Characters. Sporozoa in which the euglena phase is dominant, being relatively of large size, elongate in form, definitely shaped, having contractile but not viscid cortex, and exhibiting often active nutritional and locomotor phenomena. Though usually if not invariably cell-parasites in early youth, they become free before attaining adult growth, and inhabit either the body-cavity or the intestine of their hosts. Many spores are produced in the encysted phase. The spores have an oblong, sometimes caudate coat, and produce each one or several falciform young. At present only known as parasites of Invertebrata. Two individuals, which are implanted by one extremity at b in two epithelial cells of the rosette of the spermatic duet, a, nucleus of the Ms, L.). Monocystis. 5. Tailed chlarnydospores of Monocyxtix swnuridig, Koll. 6. Two Jtf. ayiiis encysted, spores forming on the surface of the protoplasm. 7. A similar cyst furtheradvanced in spore-formation (see Fig. XVIII.). 8. Spore of M. atjilia, now elongated but still naked. a, nucleus, x 1400. 9. The spore has now encased itself in a navicula- sliaped coat, a, nucleus. 10. The spore protoplasm has now divided , , . . e oe proopasm as now ve into several falciform swarm-spores, leaving a portion of the protoplasm unused, b, Schneider s residual core. 11. Optical transverse section of a completed spore, b, Schneider s residual co e. 12. Chlamydospore 16. Alonocytstin sxnuridis, Koll., two indivi , . . duals adhering to one another (a syzygium). FIG. XVII. Sporozoa. 1,2. Monocystis agills, Stem; x250; from the testis of the Earthworm. Two phases of movement a ring-like contraction passing along the body from one end to the other. 3. Individual of the same species which has penetrated in the young stage a sperm-cell of the Earthworm, and is now clothed as it were with spermatoblasts. 4. Monocyatiii inajna, A. Schmidt, from the testis of the Earthworm [L. terres- Klonsia helicina, the contents broken up into spherical ehlamydo- spores. 20. Single spore from the last, showing falciform young and a Schneider s residue b. 21. The contents of the same spore. 22. A small renal cell of Helix containing two of the youngest stage of Klossia. 23. Monocystis sa/jittata, Leuck., from the intestine of Capitella capitata ; x 100. 24 to 31. Coccidium oviforme, Leuck., from theliver of the Rabbit 24, adult individual encysted ; 25, the protoplasm contracted a, nucleus ; 26, 27, division into four spores, as yet naked ; 28, 29, the spores have acquired a covering, i.e., are clilamydi spores, and each contains a single falciform young ; 30, 31, two views of a chlamydospore more highly magni fied so as to show the single falciform young (from Leuckart). 32. Klossia octopiana, Aim. Schu., from Cephalopoda, a, nucleus; b, cyst-membrane, x 200 diani. 33. Single spherical spore of the same ; x 1400 diam ; showing numerous falciform young, and b, Schneider s residue. A uo uiain. oo-,}:/. j^n/ti i <n j(t<.ct t iui nits, TJIII -* , -- 35, an adult non-encysted individual inhabiting an epithelial cell of the intestine of the mouse ; 36, encysted phase ; 37, clear corpuscles appear in the encysted protoplasm ; 38, the protoplasm now forms a single spore containing several falciform young ; b, Schneider s residue ; 39, isolated spore showing falciform young, and b, Schneider s residue. 40. Chlamydospore of Myxobolm Miilleri, Biitschli, one of the Myxo- sporidia from the gills of Cyprinoid Fishes, a, nucleus ; b, refringent corpuscle ; c, polar liody or thread-capsule. 41. A similar chlamydo spore which has ejected the filaments from its thread capsules. 42. Chlamydospore of a Myxosporidium infesting the kidney of Lota vulgaris. c, polar body (psorosperm of authors). 43, 44. Chlamydospores of a Myxosporidium from the gills of Perca (psorosperm of authors). Compare with the tailed chlamydospore of Monocjixtis ssenuridis, 5. 45 -47. Drepanidium ranarum, Lankester, the falciform young of an unascertained Coccidiide infesting the Frog (supposed by Gaule to be pro duced by the blood corpuscles) : 45, specimen stained by iodine ; 46, red- blood corpuscle of Frog, showing b, two contained Drepanidia, and a, the nucleus of the blood corpuscle ; 47, living Drepanidium. 48. Chlamy dospore of Lieberkuhn s Coccidium of the Frog s kidney, perhaps belong ing to the life-cycle of Drepanidium ranarum. The spore contains two falciform young (Drepanidia?) and a Schneider s residue. Chlamydospore of Monocyatis lhalaxsemni, Lankester, containing nume rous falciform young. 50, 51. Sareoeystis Miescheri, Lankester: 50, falciform young escaped from chlamydospores ; 51, adult euglena phase inhabiting a striated muscle fibre of the Pig. OKDER 1. HAPLOCYTA, Lankester. Characters. Gregarinidea in which there is never at any time a partition of the medullary substance into two or more chambers. The euglenoid is always a single contractile sac with one mass of medullary substance in which floats the large vesicular transparent nucleus. Spores larger than in the next group, each producing several falciform young. Genus unicum. Monocystis, Stein, 1848. The various generic subdivisions proposed by Aim. Schneider (48), and accepted by Biitschli, appear to the present writer to have insufficient characters, and serve to complicate rather than to organize our knowledge of the subject. We do not yet know enough of the sporulation and subsequent development of the various monocystic Gregarinides to justify the erection of distinct genera. Monocystis agilis, Stein, Fig. XVII. 1, 2, 3, 6, 7, 8, 9, 10, 11, and Fig. XVIII. is the type. The other species of Monocystis occur chiefly (and very commonly) in marine Annelids, Platyhel- minthes, Gephyraa, and Tunicata ; not in Arthropoda, Mollusca, nor Vertebrata. The only definite differences which they present of possibly more than specific worth, as compared with M. agihs, are in the form of the chlamydospores, which are sometimes tailed, as in M. stenuridis (Fig. XVII. 5), and in M. nemertis (Fig. X II. 13) and M. sipunculi, and further also certain differences in the general form, as for instance the anchor-like M. sagittata (Fig. XVII. 23), and the proboscidiferous M. aphrodite (Fig. X II. 17). The fine parallel striation of the cuticule in some species (M. serpidie, &c.) might also be made the basis of a generic or sub- generic group. On the whole it seems best to leave all the species for the present in the one genus Monocystis, pending further knowledge, probable that more than one species (at least two, M. acjihs and M. magna) infest the common Earthworm. ORDER 2. SEPTATA, Lankester. Characters. Gregarinidea in which in the adult the medullary
substance is separated into two chambers a smaller anterior (the