III. SPOROZOA 



185 



by a pit at one point, tlie cytostome, near which is the nucleus surrounded by an 

 aggregation of protoplasm which sends branching threads into the jelly of the 

 body. At the entrance to the cytostome is a fiagellum, used in feeding but not 

 in locomotion, and a band-like tentacle consisting of an outgrowth of the body 

 membrane with a transversely banded muscular axis; it moves slowly with a 

 swinging motion, Noctiluca reproduces by simple fission (progamic repro- 

 duction) and by formation of swarm spores ( ? mctagamic reproduction) (fig. 144, 





Fig. 144. — Noctiluca millaris (in part aiter Cienkowski). A, entire animal;/, 

 fiagellum; 11, nucleus; 0, cytostome, beside it the 'tooth' and 'Up'; <, tentacle; B, C, 

 upper end \\ith two stages in the formation of zoospores; D, zoospores. 



B, C, D). In the latter two individuals lose tentacles, flagella, and cystos- 

 tomes, and conjugate; after mutual nuclear fertilization ( ?) the animals separate, 

 while the protoplasm in each collects in a disc which, by successive divisions, is 

 converted into numerous uninucleate oval germs which at first project from 

 the sphere, then separate and form small flagellate spores whose history is not 

 known. Leptodiscus mcdusoides of Europe looks and swims like a small medusa. 

 Craspedotdla/* 



Class III. Sporozoa. 



The Sporozoa are exclusively parasitic, and this has modified their 

 feeding, movements and reproduction and in very similar ways. ]\Iany 

 of them live as parasites in cells ('Cytosporida') as long as their size will 

 permit; and after they have left the host cell, they live on fluid, not on solid 

 food, hence they lack all arrangements for taking food, even in those cases 

 where the body is covered with a cuticle. As a rule, there is also a lack of 

 locomotor structures; but the occasional presence of amoeboid motion or 

 flagella indicates a near relationship with rhizopods and flagellates, so 

 that it is difficult to draw sharp lines between the three classes. There are 

 very close relations between the parasitic flagellates (Trypanosomes) 

 and the Hfemosporida, and the Sporozoa must be regarded as rhizopods 

 or flagellates modified by parasitism. 



It is characteristic of the reproduction that the developmental stages before 

 and after fertilization — pro- and metagamic — have different characters. The 



