THE SPOJKOZOA 



157 



without fusing. The nuclei of the two cells then divide by mitosis, 

 and in each case one of the daughter-nuclei is thrown off as a useless 

 moiety in the same way as a polar globule. The other two daughter- 

 nuclei move toward the partition wall which separates the two 

 individuals, and meet each other in an opening of this wall. They 

 fuse, and this fused mass divides by mitosis, one of the daughter- 

 halves going to each of the conjugants. The nuclei then divide 

 repeatedly, and spores are formed in the usual manner. This 

 method if correctly observed, in contradistinction to pseudoconjugation 

 among the Gregarinida and Haemosporidiida, is nuclear conjugation 

 as seen in its highest development among the Infusoria ; but, unfortu- 

 nately, there are no observations similar to those of Biitschli, Engel- 



'" f ; 



Fig. 87. Monocystis ascidice Lankest. [SlEDLECKI.] 



A. Fusion of two individuals. B. Formation of gametes (cf. Fig. 84). C. Nuclear division after 

 the fusion of gametes, and sporozoite formation. 



mann, Maupas, and others on Infusoria to indicate the significance, 

 and the facts themselves rest upon the observation of a single observer 

 (VVolters). In a closely related form (Monocystis ascidia), Siedlecki 

 ('99) describes an entirely different process. Here two individuals 

 come together in a single cyst, within which each forms a number of 

 merozoites or gametes. The gametes fuse together, and thus affect 

 the conjugation of the two original individuals (Fig. 87). 



The greatest advances in our knowledge of the reproduction in 

 Sporozoa, during the last ten years, have been in connection with the 

 Coccidiida, and modern research has shown that the life-history of these 

 forms is bound up with a complicated alternation of generations, the 

 product of the union of sex-cells being the permanent spores by 

 which the infection is carried from one organism to another, while 

 the products of asexual increase lead to auto-infection within the 

 same host. 



Up to the last five years the usual description of the life-history of 



