COCCIDIIDEA 141 



gamete that has gained entry unites with the nucleus of the macro- 

 gamete, which latter is afterwards capable of forming the well-known 

 spores. The parasite is now called an encysted zygote or oocyst. The 

 oocysts of some other members of the Coccidiidea, e.g., Ehneria avium, 

 can form their walls prior to fertilization. In such cases, a weak spot 

 is left at one place in the cyst wall, forming a micropyle, that permits of 

 the entry of the male, immediately after which the micropyle is closed. 



The reduced nucleus of the macrogamete elongates on the entry of the micro- 

 gamete, and becomes a fertilization spindle to which the male pronucleus (from the 

 microgamete) becomes attached (fig. 67, XIV and xv). Thereupon the spindle 

 divides into two daughter nuclei (fig. 67, xvi) which assume a round shape. The 

 protoplasm at this stage may at once divide, or another segmentation of the daughter 

 nuclei may first occur. In the former case the two halves divide again, so that 

 finally four nucleated segments, the sporoblasts, are formed, whereas in the latter 

 case the four sporoblasts appear simultaneously (fig. 67, XVli). In both cases a 

 residual body of varying size is separated from the protoplasm of the oocyst. As 

 a rule the oocysts have already been discharged from the body of the host, and in 

 the manner described above, form the sporoblasts after a longer or shorter period 

 of incubation. 



The sporoblasts are originally naked, but each soon secretes a 

 homogeneous membrane, the sporocyst, in which it becomes enveloped 

 (fig. 67, xvin). After the segmentation of the nucleus the contents 

 divide into two sickle-shaped sporozoites, in addition to which there 

 is generally also a residual body (fig. 67, xix). 



This terminates the development. The spores are intended for 

 the infection of other hosts. If they reach the intestine of suitable 

 hosts, either free or enclosed in the oocyst wall, the action of the 

 intestinal juices causes them to open and permits the escape of the 

 sporozoites (fig. 67, xx). The latter move exactly like the merozoites 

 and soon make their way into epithelial cells (fig. 67, i), where they 

 become schizonts, and thus repeat the life cycle. 



Although our knowledge of the development of the coccidia is but of recent date, 

 yet it already extends to a large number of species, which exhibit various deviations 

 from the cycle of development described above. For instance, in addition to 

 differences in the gametocytes, the schizonts of Adelea and Cyclospora also show 

 differentiation and give rise to macromerozoites and micromerozoites, whilst in 

 Adelea and Klossia a precocious association of the gametocytes precedes the true 

 copulation of the ripe gametes. 



The classification of the Coccidiidea is based chiefly on the 

 number of sporozoites found in each spore, and the number of 

 sporocysts (spores) found in one oocyst. Leger 1 recognises two 

 great legions, the Eimeridea and the Adeleidea, the former comprising 

 the greater number of genera, including the genus of most economic 

 importance, Eimeria. It must be noted that, though a member of 



1 Arch.f. Protistenkunde (1911), xxii, p. 71. 



