MYXOBOLUS PFEIFFERI 



29 



the two polar capsules. The two gamete nuclei come to lie in a cyto- 

 plasmic body at the posterior part of the spore. Finally, the two gamete 

 nuclei fuse. Apparently, the spores escape into the water and are ingested 

 by fish. The amoeboid body presumably escapes from the spore and 



Fig. 308. 



-Development of the Spores of Myxobolus pfeifferi from the 

 Pansporoblast (x 2,500). (After Keysselitz, 1908.) 



1. Single propagative cell formed from the multinucleate plasmodium. 



2. Division to form one large and one small cell. 



3. Association of two pairs to give a group of two large and two small cells. 



4-5. Formation of six-cell stage. Each small cell which does not multii^ly tends to spread a 

 covering over its own sister cells. 



6. Stage with fourteen nuclei, two of which are the nuclei of the original small cells. 



7. Division into two bodies, each with six nuclei, while the nuclei of the small cells take up a 



position at the angles between them. 



8. Each body now divides into three cells, two of which, with single nuclei and vacuoles, 



form the polar capsules, one with two nuclei the infective agent, while two nuclei 

 become peripherally arranged and form, together with some cytoplasm, the valves of 

 the spore. 



9. More advanced stage of one of the developing spores shown in 7. 

 10- U. Fully developed spores. 



finds its way to the tissues of the fish, in which it develops into the multi- 

 nucleate Plasmodium. As is to be expected, the tracing of this part of 

 the development is beset with many difficulties. Other observers, such as 

 Schuurmans-Stekhoven (1919), state that there is no syngamy. 



