THE GREGARINES AND COCCIDIA 349 



two flagella, both arising at the anterior end and directed forwards. In 

 Coccidium rouxi, Elmassian describes two forms of microgametes differing 

 greatly in size. 



In forms in which the sporonts associate, as in Adelea and Orcheobius, one 

 of the four microgametes produced penetrates the macrogamete ; the other 

 three die off. In some species e.g., Coccidium proprium of the newt the 

 oocyst is formed prior to fertilization, and the male gamete enters through a 

 minute aperture or micropyle, which is closed as soon as one has entered. 

 In Cydospora caryolytica, however, numerous microgametes penetrate into 

 the macrogamete, but only one of them furnishes a male pronucleus, which 

 copulates with the female pronucleus ; the remaining male nuclei are absorbed. 



A fertilization-spindle appears always to be formed in the process of 

 syngamy, but may differ considerably in appearance from that seen in 

 C. schubergi ; compare Kunze's description of the fertilization of Orcheobius 

 herpobdellce. 



8. The zygote is enclosed, as stated above, in an oocyst 

 (Fig. 152, J) secreted at its surface as a membrane delicate at first, 

 but very soon becoming thickened to a tough impervious capsule, 

 in which the parasite can pass out of the body of the host and brave 

 the vicissitudes of the outer world. The synkaryon divides in the 

 genus Coccidium into four nuclei (Fig. 52, p. 106), and the body 

 of the zygote then divides into as many sporo blasts, each with a 

 single nucleus, leaving over a certain amount of residual protoplasm 

 (" cystal residuum "). Each sporoblast secretes a sporocyst at 

 its surface (Fig. 152, A T ), and within the envelope the sporoblast- 

 nucleus divides into two. after which the cytoplasm segments round 

 each nucleus to form two sporozoites (Fig. 152, 0), leaving a small 

 amount cf residual protoplasm (" sporal residuum "). These 

 residua are slowly absorbed. When sporogony is complete, there- 

 fore, the tough oocyst contains four spores, each consisting of a 

 tough sporocyst containing two sporozoites. In order to develop 

 further, the cyst must be swallowed by a new host, in the digestive 

 tract of which the oocyst dissolves, and the spores split open, libera- 

 ting the sporozoites. 



In other species of coccidia the details of the spore -formation may vary 

 enormously as compared with the example described. The contents of the 

 oocyst may divide into only two, or into a very large number of sporoblasts. 

 In the genus Caryospora (Leger, 644) and Cryptosporidium (Tyzzer). the 

 oocyst does not divide into sporoblasts, but gives rise to a single spore, contain- 

 ing eight sporozoites in Caryospora, four in Cryptosporidium. In Paracoccidium 

 prevoti sporocysts are formed in the oocyst. but absorbed again, so that the 

 sporozoites finally lie free in the oocyst, as in the genus Legeretta, in which no 

 sporocysts are formed at all, but the body of the zygote divides directly into 

 sporozoites. With these exceptions, resistant spores are always formed, in 

 numbers varying from two to some thirty or so in different genera. 



The spore may contain one. two, three, four, or n sporozoites, and is then 

 said to be monozoic, dizoic, trizoic, tetrazoic, or polyzoic ; it is rarely octozoic, 

 as in gregarines, but Caryospora is so. In Caryotropha mesnilii the spore 

 contains twelve, in Angeiocystis audouinice about thirty sporozoites (Brasil, 

 597). In contrast also with gregarines, the spores of coccidia are generally 

 smooth, round, or ovoid bodies, but in a few cases (e.g., Minchinia chitonis) 

 bear tails or spikes. 



