436 BIOLOGY OF THE PROTOZOA 



duction. Change of hosts with alternation of generations while 

 by no means universal, is more common than in the Gregarinida. 

 Agamogony is characteristic of all types and leads to multiple 

 infection with frequently lethal results to the host due to the 

 destruction of multitudes of epithelial or blood cells, to thrombus 

 formation, or to the liberation of toxins. The life cycle varies 

 from relative simplicity to great complexity; gamonts become 

 differentiated into gametoc^les which may be recognized as male 

 and female; gametes are anisogamous with rare exceptions; zygotes 

 give rise to sporoblasts which may (Coccidia) or may not (Ha;mo- 

 sporidia) be protected by resistant membranes. The presence or 

 absence of sporoblast capsules is of primary importance in the 

 mode of life and the life history, and affords an excellent basis for 

 the natural classification of the group into two Orders, Coccidia 

 and Hsemosporidia, epithelium and blood-dwelling parasites respec- 

 tively. 



Order 1. Coccidia, Leuckart, Em. 



Typically epithelial-cell dwelling parasites with encapsulated 

 sporoblasts. Exceptions to both generalizations, however, are 

 known; thus Cryptosporidium vturis, Tyzzer; FAmeria mitraria, Lav. 

 and Mesn., and Orcheiohiiis hcrjHMdJoc, Kunze, are lumen-dwelling 

 coccidia, while in Dobellia and in Legrrclla sporoblast capsules are 

 absent. Hemogregarines are not epithelial cell parasites but live 

 in blood cells both leukocytes and red cells. In other respects the 

 group is fairly homogenous and the life history as outlined on p. 418 

 is typical for practically all species. Variations in details as for 

 example time (before or after fertilization) of formation of the 

 sporocyst capsule, number of sporoblasts formed by the zygote, the 

 presence or absence of a residual body in sporocyst or sporoblast, 

 and the number of sporozoites in a sporoblast are useful in dis- 

 tinguishing genera and species. 



Anisogamous gametes are typical throughout the group. In some 

 cases they approach the gregarine type with pseudoconjugation, 

 although ' cyst membranes are not formed. Thus in Adeleidse, 

 some types, for example Adeka and Dobellia, are represented by 

 gametocytes which come together in pseudoconjugation; one, the 

 microgametocyte undergoes nuclear division until usually four 

 (more in Dobellia) microgamete nuclei are formed. One of these 

 nuclei penetrates the macrogamete and fertilizes it. In other cases 

 fertilization is brought about by wandering flagellated microgametes. 



Cellular differentiations are much less numerous than in the 

 gregarines, particularly is this true of the cortex. They are motion- 

 Fess forms without myonemes or other motile organs save flagella of 

 the microgametes, and cellular processes are generally absent. The 

 endoplasm is usually well stored with products of metabolism some 



