IV. SPOROZOA: COCCIDIAE. 215 



anchorage, and is lost when the animal gives up its connexion 

 with the host cell. Among the intestinal gregarines frequently 

 occur l associations ' where two or more animals are fastened to- 

 gether head to tail in a row. Perhaps these associations are prep- 

 arations for conjugation which occurs in development. 



Eeproduction occurs exclusively in an encysted condition (fig. 

 155, II, ^4). Usually two animals (sometimes one, rarely more than 

 two) occur in a cyst. A fusion of the two encysted animals does 

 not take place, but it is probable that a nuclear exchange (recalling 

 that of ciliates) takes place. After each individual has become 

 polynucleate by division of its nucleus, it divides at first super- 

 ficially, later internally into small particles, the sporoblasts (II, B), 

 which change into spores, here called pseudonavicellae. The 

 pseudonavicellae are inononucleate bodies with firm membrane and 

 usually spindle form in shape (III, AA). In these processes a 

 part of the gregarine takes no part. This residual body appears 

 under proper conditions to swell up and rupture the cyst, thus 

 freeing the pseudonavicellae. In many gregarines there are sporo- 

 ducts for the escape of the pseudonavicellae (fig. 154, A). The 

 contents of the pseudonavicellae divides into (usually eight) sporo- 

 zoites or falciform spores which must pass out from the spores and 

 into the cells of the host in order to form gregarines. This escape 

 of the sporozoites depends upon entrance into the proper host. 

 Often the transformation of the contents of the cysts into pseudo- 

 navicellae takes place when the cysts have left the original host. 



Best known are the Monocystis tenax of thespermatheca of earthworms, 

 and Gregarina (Clepsidrina) Uattarum of the cockroach. The American 

 species have scarcely been touched. One species is abundant in the intes- 

 tine of Geophilus. 



Order II. Coccidiae. 



The gregarines of all Sporozoa are nearest the Coccidiae, which 

 are also cell parasites with a single nucleus, but without either cell 

 membrane or division into protomerite and deutomerite. In most 

 species, as in Coccidium cuniculi, there are two types of reproduc- 

 tion, an endogenous, leading to ' autoinfection/ and an exogenous, 

 concerned in the transfer of the germs to other hosts. In the 

 first (lacking in many species) the Coccidium divides into many 

 falciform germs which separate from each other and, without 

 alternation of hosts, enter other cells. The second type is begun 

 by fertilization. Certain individuals, by rapid division form 

 microgametes, small bodies swimming with serpentine motions or 

 by one or two flagella. Other individuals do not divide, but form 



