212 



THE CELL 



method of nuclear multiplication, to which I should like to attach 

 the above name, has been observed by Richard Hertwig (VI. 36) 

 amongst a group of Radiolarians, the Thalassi colli dee ; these ob- 

 servations have been corroborated by Carl Brandt (VI. 8), who 

 has followed them up in greater detail. 



The Thalassicollidte, which are the largest in size of all the 

 Radiolarians, the diameter of their central capsule being nearly as 

 long as that of the Frog's egg, possess during the greater part 

 of their lives one single highly differentiated giant nucleus, the 

 so-called internal vesicle ; this is about | mm. in diameter, and 

 possesses a thick porous nuclear membrane. It is very similar to 

 the multinucleated germinal vesicle of a Fish or of an Amphibian. 

 A large number of variously shaped nuclein bodies, generally 

 compressed together into a heap in the centre, are present in its 



interior (Fig. 105). Amongst these, a 

 bright central corpuscle (centrosome), 

 surrounded by a radiation sphere, may 

 very frequently be seen. This was 

 observed and depicted by R. Hertwig, 

 and has recently been more clotely in- 

 vestigated by Brandt. The latter ob- 

 server was able to follow how, at the 

 time of reproduction, the centrosome r 

 which appears to me to correspond 

 with the body of that name in plant 

 and animal cells, betakes itself to the 

 surface of the internal vesicle, drawing 

 the radiation sphere after it. Here, 

 after passing through the nuclear 

 membrane, it enters into the surround- 

 ing protoplasm of the central capsule ; 

 however, as yet nothing has been re- 

 ported as to its further fate. 



About this time a large number of 

 small nuclei make their appearance 

 outside of the internal vesicle, being 

 situated in the protoplasm of the cen- 

 tral capsule, which originally was quite 

 free from nuclei ; these function as 

 centres around which nucleated zoospores develop, whose number 

 finally may amount to some hundreds of thousands. Meanwhile, 



Fig. 105. A small portion of a 

 section through a great vesicular 

 nucleus, the so-called internal 

 vesicle of Thalassicolla nucleata 

 with funicular internal bodies 

 (nuclear bodies) which radiate 

 from a common point. (R. Hert- 

 wig, PI. V., Fig. 7.) 



