MYXOSPORIDIA 319 



The fact that the generative nucleus divides by mitosis, has been 

 known since Thelohan's work. The process has been observed by 

 subsequent investigators in both coelozoic and histozoic species. 



The trophozoites multiply in number. In coelozoic forms, plas- 

 motomy (Doflein, 1898) has been noted to occur in several species 

 (Laveran and Mesnil, 1902, Georgevitch, 191 7, 1919, etc.). Multi- 

 plication by budding or gemmation has also been noted by Cohn 

 (1895), Davis (1916), Georgevitch (1917), Kudo (1922), Bremer 

 (1922), and others. In the histozoic form, the trophozoite is con- 

 sidered as capable of multiplication, but exact information as to 

 how and when this occurs is still lacking. 



11. Problems concerning the origin of tJie sporoblasf or pan- 

 sporoblast. All investigators are agreed that the earliest develop- 

 mental stage is a uninucleate amoebula found in the intestine or 

 blood stream of the host body. As to the origin of the pansporo- 

 blast formation, there are many and diverse views, which may be 

 put under the following general groups : 



a) Each generative nucleus becomes a sporoblast or a pansporo- 

 blast by being surrounded by an island of cytoplasm and the 

 nucleus gives rise by repeated divisions to several nuclei to form 

 one or two spores. 



b) A pansporoblast is formed by union of two cells. In this, 

 three groups of opinion are to be distinguished : 



(1) By union of two uninucleate gametes. 



(2) By union of two binucleate cells, the nuclei of each of 

 which were formed by a division of a single nucleus. 



(3) By union of two binucleate cells, each of which was formed 

 by cytoplasmic fusion of two uninucleate bodies. 



Up to the present time, no one has succeeded in observing the 

 changes which take place in the trophozoite and which result in 

 the formation of the sporoblast or pansporoblast in the living state 

 and the views summarized above of various investigators were 

 based exclusively upon careful studies of various phases as seen in 

 permanent preparations. 



12. Problems concerning the developing sporoblast and pan- 

 sporoblast. In some forms in which a single generative nucleus 

 gives rise to a single sporoblast, the nucleus presumably divides 

 into two ; one small nucleus remains as the vegetative nucleus of 

 the sporoblast, while the large nucleus divides repeatedly to 

 produce from six (in bicapsulated spore) to eight (in tetracapsu- 



