546 BIOLOGY OF THE PROTOZOA 



polar capsules containing coiled threads, 1 is cast out of the 1 cell 

 and 2 remain as the gametic nuclei which, sooner or later, unite to 

 form one, a process of fertilization frequently interpreted as autog- 

 amy (Fig. 164, p. 325). 



Sexual processes in Cnidosporidia are so unlike analogous phe- 

 nomena in other Protozoa that they have long been a puzzle to 

 cytologists as well as matters of controversy to a long list of special- 

 ists (Debaisieux, Erdmann, Kudo, Parisi, Auerbach, Merrier, 

 Keysselitz, Schroder, Davis, et at.). Thanks to the splendid mono- 

 graph by Naville (1931) there is a fair prospect that the difficulties 

 will be solved and unanimity established although the phenomena 

 are quite diverse and, in comparison with other Protozoa, most 

 aberrant. 



The cnidosporidian trophozoite is an ameboid organism with 

 multiple nuclei and may reproduce by division or by budding 

 (schizogony). There is no alternation of sexual and asexual cycles 

 but the sexual generation is contained in the protoplasm of the 

 trophozoite which develops from a sporozoite. 



The activities of the sexual generation are confined to internal 

 buds or spore-forming centers termed pansporoblasts by Gurley 

 (1893). Two nuclei are present at the outset in these endogenous 

 buds and each undergoes division until 14 are present, 7 from 

 each of the original nuclei. The bud then divides into 2 cells, 

 each of which is a sporoblast and each contains 6 nuclei, 1 having 

 been cast out. Two of these 6 form capsules (sporocysts) , 2 form 

 nematocysts and 2 remain as pronuclei which subsequently fuse. 



From this history it would appear that the endogenous bud 

 represents a zygote and the 2 original nuclei progamete nuclei. 

 Obviously the significance of these nuclei depends upon their pre- 

 vious history. The facts in such histories for different species have 

 been variously interpreted by earlier investigators and find a place 

 in Naville's interpretation. This is based upon his independent 

 study of five different species of Myxosporidia (Myxobolus guyenoti, 

 Chloromyxum leydigi, Myxidium incurvatum, Sphaeromyxa balbianii 

 and Sphaeromyxa sabrazesi). In all these species the early divisions 

 of the trophozoite nuclei indicate that there are two types as shown 

 by the mitotic figures. One type respresents germinal nuclei with 

 diploid number of chromosomes in the typical division figure. The 

 other type represents vegetative nuclei which divide by amitosis 

 (Naville) or by cryptomitosis (Reichenow). The germinal nuclei 

 after several divisions with the diploid number of chromosomes 

 undergo reducing divisions whereby the number of chromosomes is 

 reduced to one-half. 



In Sphaeromyxa sabrazesi (Fig. 104, p. 325) the two original 

 nuclei of the pansporoblast are different in size. According to 

 Naville this results from two lines of germinal nuclei. In one line 



