332 



SPOROZOA. 



Sporulation begins with a peculiar process of endogenous 

 or internal budding. An island of protoplasm or pansporo- 

 blast is formed round two of the nuclei, which are usually 

 dimorphic. Each of these nuclei undergoes division until 

 fourteen are present, seven from each of the original nuclei. 

 The bud then divides into two cells, each of which is a sporo- 

 blast containing six nuclei, after one has been extruded. 

 Two of these six nuclei form the valves of the capsule (sporo- 

 cyst), two form the polar capsules, and two remain as pro- 

 nuclei, which subsequently fuse when the spore becomes 

 mature. Thus the endogenous bud represents a zygote, 

 and the two original nuclei of the pansporoblast the pro- 

 gametic nuclei. The details of the process of sporulation 



B 



Fig, 166. — External appearance of Myxosporidian infection in jSsh. 

 A, head of the short-headed red-horse, showing the cysts 

 of Myxobolus conspicuus Kudo, x J ; -B, the river chub, 

 with cysts of Myxobolus squamosus Kudo, X f ; C, a blunt- 

 nosed minnow, with numerous cysts of Myxobolus aureatus 

 Ward on the fins, x f . (After Kudo.) 



differ in different species. Neville (1931) has reviewed the 

 previous literature and made an independent study of five 

 different species. He concludes that there are two types of 

 nuclei, germmal and vegetative. The germinal nuclei contain 

 the diploid number of chromosomes, but after several divisions 

 undergo reduction, whereby the number of chromosomes is 

 reduced to one-half. 



The simpler members of the order occur in various cavities 

 in the bodies of their host, such as the gall-bladder, uriniferous 



