318 THE SPOROZOA 



they may infect the eggs and embryos of the host, in which the mantle- 

 cavity acts as a brood-pouch. No other stages of the parasite have been 

 observed, since the spindle-shaped variety first described by Plate has 

 been found by him, on renewed investigation, to be in reality a patho- 

 logically modified form of the nuclei of the supporting cells of the mucous 

 frills. Since no method of sporulation has been shown to occur, this 

 parasite cannot as yet be enrolled amongst the Sporozoa. 



Karyamoeba, Giglio-Tos, 1900, for K. renis, G.-T., an intranuclear 

 parasite (?) of the renal epithelium of Mus decumanus. 



Nematopsis, A. Schneider, 1892, for N. sp., parasite of the connective- 

 tissue cells of the mantle of Solen vagina. A single host-cell may contain 

 one, two, or three cysts, in each of which is lodged a little coiled-up 

 animalcule, resembling a tiny Nematode, but consisting apparently of a 

 single cell with one nucleus. 



Schewiakoff, in 1893 [135], described, but without naming them, 

 certain " entoparasitic tubes " (Schlauche) occurring in Cyclopidae (Cyclops 

 and Diaptomus spp.), where they had been discovered by SchmeiL These 

 parasites occur as amoebae, free in all parts of the body-cavity (haemocoele) 

 of the host. The amoebae (Fig. 127, a, 6) vary in size from about 7 /x in 

 length by 3 /x in breadth, to 20 /x by 6 /x ; they send out lobose pseudo- 

 podia, and possess each a vesicular nucleus and a contractile vacuole, a 

 point in which they differ from all known Sporozoa. The contractions 

 of the vacuole take place at intervals of about 30 seconda The amoebae 

 creep over the epithelial cells and the muscles ; and they were observed 

 to fuse with one another to form plasmodia (Fig. 127, h, i, j), varying in 

 size according to the number of individuals thus united. Since sometimes 

 plasmodia formed of two or three amoebae were observed later to contain 

 only a single nucleus, it is highly probable that nuclear fusion also takes 

 place in them. After a certain time encystment takes place, either of 

 single amoebae or of plasmodia. In the former case the cysts are 

 spherical (Fig. 127, c, d), containing one nucleus, and the contractile 

 vacuole, which is visible for some time, its pulsations becoming slower. 

 The cyst -membrane has a double contour. The nucleus now becomes 

 divided up (Fig. 127, ), and the protoplasm becomes centred round the 

 daughter-nuclei to form oval spores (Fig. 127, /, g). The plasmodia 

 become encysted in a similar manner, but the cysts formed by them are 

 larger and oval in form, and the breaking up of the nucleus and other 

 preparations for spore-formation may take place while the plasmodia are 

 still free (Fig. 127, j, k, I). The spores are formed progressively in 

 the cysts ; a cyst formed from a single amoeba was observed to contain, 

 in about ten hours after the division of the nuclei was complete, six 

 spores imbedded in protoplasm containing numerous free nuclei ; twenty- 

 four hours later the number of spores was doubled, with undifferentiated 

 protoplasm and free nuclei still present in the cyst ; and after another 

 twenty-four hours the cyst was entirely filled by spores, with no residual 

 protoplasm or nuclei. The spore-formation in plasmodial cysts took 

 place in a similar manner. Each spore arises as a condensation of the 

 protoplasm round a free nucleus, and when fully formed is an oval or 



