THE GREGARINES AND COCCIDIA 351 



The germination of the spore takes place always, apparently, in the digestive 

 tract of the specific host, and there alone ; it may be in some special part of 

 it, as in G. cuniculi, the spores of which, according to Metzner, germinate in 

 pancreatic, but not in gastric, juice. 



The remarkable form Selenecoccidium intermedium (Pig. 155), parasitic 

 in the intestine of the lobster, described by L6ger and Duboscq (646), differs 

 from all other known coccidia in the character of its trophozoites and its 

 schizogony. The trophozoites are vermiform, nematode-like organisms, 

 extremely active in their movements, and frequently coiling themselves up 

 and wriggling like worms (Fig. 155, A Z>). The anterior end of the body is 

 blunt, the posterior pointed ; the surface of the body contains myonemes 

 running spirally, visible in the living state at the anterior end as oblique 

 striations. The youngest trophozoites have a single nucleus, but as they 

 grow the nuclei multiply, until in the full-grown organism there are eight. 

 The trophozoite is now a schizont, and penetrates into an epithelial cell of the 

 intestine in order to multiply by schizogony. The vermiform body rolls up 

 within the cell into a compact oval mass (Fig. 155, E), and then each of its 

 eight nuclei grows out into a tongue-like cytoplasmic process. In this way 

 eight merozoites are formed round a central residual mass. The merozoites 

 are set free as the uninucleate trophozoites (Fig. 155, F, O). This "in- 

 different " type of schizogony may continue for several generations, until a 

 final generation appears in which the schizonts are sexually differentiated; 

 smaller, slender trophozoites with eight nuclei give rise to eight merozoites 

 which grow into male sporonts, and larger, stouter forms with four nuclei 

 produce four merozoites which become female sporonts. 



The male sporonts (gametocytes) arise from vermicules with clear cytoplasm, 

 which penetrate into an epithelial cell and roll up into an ovoid mass 

 (Fig. 155, H) ; they may do this when they have but a single nucleus, but 

 usually not until the nuclei have increased to eight. In the compact, intra- 

 cellular gametocyte the nuclei multiply rapidly in a manner similar to that 

 described above for the schizont of Adelea, by binary or multiple fission 

 following division of the karyosome. In later stages of multiplication the 

 karyosomes become very small, and the peripheral chromatin of the nuclei 

 increases greatly, so that they have the appearance of patches of granules 

 (Fig. 155, 1). When the multiplication is complete, each such patch of granules 

 forms the dense, comma-shaped nucleus of a microgamete (Fig. 155, J). An 

 enormous number of mierogametes arise from each gametocyte, but the 

 structure of the free mierogametes has not been made out. 



The female gametocytes arise from stout vermicules which penetrate into 

 a cell and become rounded off, the nucleus remaining single all the time 

 (Fig. 155, K, L, M). The oval gametocyte grows, and its cytoplasm becomes 

 full of chromatoid grains. When full-grown it appears to go through a process 

 of maturation, in which, as in Adelea, the karyosome divides into two, and one 

 half is expelled. The full details of the fertilization have not been made 

 out, but macrogametes have been seen with the nucleus placed superficially, 

 and with a small corpuscle, apparently a microgamete, adherent to the body 

 (Fig. 155, N). After fertilization the zygote becomes spherical and surrounds 



FIG. 155. Selenococcidium intermedium : various phases in the life-cycle. A, B, 

 C,D, Vermicules with one, two, five, and eight nuclei respectively ; E, vermi- 

 cule rolling up prior to schizogony ; F, schizogouy nearly complete ; eight 

 pear-shaped merozoites, each with a single nucleus, budded off from a mass 

 of residual protoplasm to which they are still attached by long stalks ; G, 

 schizogony complete ; eight uninucleate vermicules rolled up together ; H, I, J, 

 formation of microgametes : H, the nuclei of the microgametocyte at an early 

 stage of division ; /, later stage ; J, formation of a great number of comma- 

 shaped microgametes ; K, L, vermicule rolling up to become a macrogameto- 

 cyte ; M , fully-formed macrogametocyte, its cytoplasm full of patches of 

 chromatoid granules that stain deeply with iron-hfematoxylin ; 2V, macro- 

 gamete at the moment of fertilization ; 0, oocyst with very numerous chroma* 

 toid grains. After Le"ger and Duboscq (646). 



