86 



ZOOLOGY 



SEOT. 



it is possible to distinguish between two sets of gametes which may 

 be looked upon as male and female, copulation taking place between 

 members of the two sets. 



The cysts of Gregarina (Fig. 63, C) are often very complex and 

 provided with delicate ducts (spd.) in the thickness of the wall, 

 through which the spores escape. In Gregarina (Porospora) 

 gigantea of the Lobster, the young (sporozoite) is liberated from the 

 spore in the form of a non-nucleated amcebula (D l ), with one long 

 and one short pseudopod (D 2 ) ; this divides by the long pseudopod 

 (psd. 2) becoming separated off, and each product of fission, develop- 

 ing a nucleus, passes into the adult (trophozoite) form (IP, D 4 ). 

 Such a multiplication by fission (schizogony) is repeated in such 

 cases through several generations till eventually a generation is 

 formed in which reproduction takes place by spore-formation ac- 

 companied by a sexual process. In other cases the sporozoites do 

 not divide, but each develops directly into the trophozoite (Fig. 64). 



ORDER 2. COCCIDIIDEA. 



Coccidium (Figs. 65, 66) and allied genera are parasites in the interior of 

 cells, both in Vertebrates and Invertebrates. They live in the cells of various 



organs, most fre- 

 quently in those 

 of the epithelium 

 of the digestive 

 canal. They 

 never inhabit 

 blood-corpuscles. 

 A few are intra- 

 nuclear parasites. 

 Two distinct 

 modes of multi- 

 plication occur 

 by schizogony, a 

 kind of multiple 

 fission, and by 

 sporogony, a pro- 

 cess of spore - 

 formation pre- 

 ceded by copu- 

 lation between 

 male and female 

 cells. The tropho- 

 zoite, or adult phase, as we may term it, of the parasite, grows to a 

 certain size within the cell without destroying its vitality the nucleus 

 merely being pushed on one side. So far, in fact, from impairing 

 the nutrition of the cell, the presence of the parasite seems, in some 

 cases, for a time, rather to stimulate it. At a certain stage of growth 

 schizogony (Fig. 66, b-c) takes place. The nucleus divides to form a 

 number of nuclei. These migrate towards the surface, and each becomes 

 surrounded by protoplasm, with the result that a number of small cells are 

 formed. Each of these gives rise to a club-shaped merozoite. The merozoites, 

 when they become free, are active bodies, which are able to penetrate into the 

 interior of other epithelial cells and develop into trophozoites like those from 



1 Eimeria 



2. Coccidium 



Fro. 65. Coceidiidea. A, adult Eimeria (E) in enteric epithelial 

 cell (ep.) of mouse ; B, encysted form ; C, encysted form, the 

 protoplasm contracting to form a spore ; D, formation of falci- 

 form young ( /.) in interior of spore (sp.) ; B, spore with falciform 

 young ; F , adult encysted form of Coccidium from liver of rabbit ; 

 G, division into spores ; H, cyst containing ripe spores (sp.), each 

 with a single falciform young ; I, single spore with falciform 

 young (/.). (From Bfltschli's Protozoa, after Leuckart and 

 Eimer.) 



