[NTRODUOTION. 



11 



Encystment without conjugation and followed by 

 division may also occur, but in this case no centrosomes 

 are formed. 



The third group consists of species having a single 

 eccentrically placed nucleus and a " central granule." 

 The processes of reproduction which take place in 



i'lG. ISO. — Successive stages of fission in AcMnophrys sol. 



AcanthocysttH acnleata are probably typical for the 

 group as a whole ; the nucleus may divide by a process 

 of mitosis or amitotic nuclear division may take place. 

 When mitotic division is about to occur in Acantlio- 

 cijfiti^ aculeata, the first sign is the division of the 

 " central granule " into two parts which separate and 

 place themselves at two poles of the endoplasm, the 

 nucleus becomes centrally placed and forms an equa- 

 torial band of chromosomes on the spindle which joins 



