28 



THE HELIOZOA 



Grenadier (6) as the " Centralkorn," has been proved by 

 Schaudinn to be a true centrosome. It has been discovered to 

 be a permanent of the body in llhaphidiophrys, Adinolophus, Hetero- 

 phrys, and Sphaerastrum. Before division of the nucleus it divides 

 into two equal parts, which take a position at opposite poles of the 

 endoplasm, each one surrounded by an aster of radiating lines. The 

 nucleus leaves its excentric position and becomes situated in a 

 direct line between the two centrosomes. The nuclear mem- 

 brane then fades away and a party of numerous small chromo- 

 somes occupy a position of an equatorial band on the spindle that 



Fio. 7. 



A, B, C, direct amitotic division of the nucleus of Acanthocystis aculeata as seen in the 

 process of the formation of buds. U, a colony of Acanthocystis formed by the gemmation of 

 a single individual. Only two individuals of the colony exhibit a centrosome, and these have 

 been formed by division, with nuclear mitosis, of the primary individuals ; the others have 

 been formed by gemmation without nuclear mitosis. E, a single bud freed from the 

 colony. F, a flagellula. G, an amoeboid spore. (After Schaudinn.) 



is formed from the linin of the nucleus. The subsequent phases 

 of the nuclear division resemble those of the typical karyokinesis 

 of the metazoan cell. 



* In the formation of the buds of Acantlwcystis the nucleus divides 

 directly and the centrosome remains unchanged (Fig. 7, A, B). 

 The buds are therefore for a time without any centrosome, but 

 this body is formed afresh in the buds from the nucleus. (See 

 Part I. Fasc. II. Fig. 20, p. 41.) 



Reproductive Processes. Probably all the higher Heliozoa are 

 capable of fission, preceded or not by encystment, although the 

 process has not been observed in all. The division of the nucleus 



