188 PROTOZOA 



That always gametes of different origin fuse is shown by Stylorhynchus 

 where the gametes of one animal are flagellate, those of another are station- 

 ary. This dimorphism is so great in the Aggregatae that filiform spermato- 

 zoids occur, as in the Coccidia. After the formation of the gametes the 

 movements of the residual body bring about the expulsion of the pseudo- 

 navicelke; and in many Gregarines sporoducts are present for their 

 escape. With repeated formation of a residual body, the contents of the 

 pseudonavicella divides into (usually eight) sporozoites or falciform spores, 

 which must leave the spores and pass anew into the tissue cells 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 pseudonavicellce takes place when the cysts have left the original 

 host. 



Best known are the Monocystis tenax of the spermatheca of earthworms, and 

 Clepsidrina blattarum of the cockroach. The American species have scarcely 

 been touched. 



Order II. Coccidiae. 



Of all Sporozoa the gregarines are nearest the Coccidiae, which are also cell 

 parasites with a single nucleus, but without either cell membrane or division into 

 protomerite and deutomerite. Best known is Eimeria stieda; (also called 

 Coccidium cuniculi and oviforme), parasitic in the liver and intestinal epithelium 

 of mammals. In the progamic development the fully grown parasite (fig. 146, 

 2) divides inside the infected cell into many cells (3, 4, 8); these separate, infect 

 other cells and begin growth and division anew (autoinfection). After this is 

 repeated several times fertilization appears (5), some parasites giving rise to 

 macrogametes, others by division forming small, actively swimming micro- 

 gametes with one or two flagella. The fertilized macrogamete or zygote (6, 7, 

 9, 10) encysts, passes out and serves to infect a new animal. Beginning earlier 

 or later, but only concluded in a new host, the contents of the cyst divide into 

 several fin Eimeria, four) sporoblast-containing spores. Each spore (7, n) 

 forms one or several (Eimeria, two) sporozoites, a residual body being left 

 behind (r). Eimeria stieda produces cheesy granules in the liver of mammals. 

 It is common in rabbits, rare in man. In cattle it is the cause of red dysentery. 



Order III. Haemosporida. 



The Haemosporida are very similar in structure and development to the 

 Coccidia. They live in blood corpuscles, and on this account and from some 

 analogies not sufficiently understood, they are regarded as related to the Try- 

 panosomes. The Haemamcebal forms parasitic in man cause malaria, there 

 being in these a progamic reproduction with autoinfection and a metagamic 

 in which the disease is transferred to another host. The parasites in the blood 

 corpuscles (fig. 147, 1-3) grow and divide (daisy form, 2), characterized by 

 little accumulations of pigment derived from the haemoglobin of the corpuscle. 

 These division products are set free by a breaking down of the corpuscle 

 (period of chill) and infect other corpuscles. This autoinfection can continue 

 a long time, until the Haemamoebae in the corpuscles grow, without dividing, to 

 'half moons' (4); these either become round and form macrogametes (5) or divide 

 into eight microgametes (6). The conjugation of these seems only to take place 



