3O2 LEONARD P. SAYLES. 



portion of the nephridia possess nucleoli of considerable size, too. 

 In fact, these cells are very similar in appearance to intermediate 

 neoblasts, from which they may be distinguished by the presence 

 of large granules in their cytoplasm (p. 288). Similarly, as 

 described by Krecker ('23), the phagocytes have very large 

 nucleoli. 



Again, in the growing tail, just as in the regenerating individual, 

 the hypodermal cells have enlarged nucleoli, particularly on the 

 ventral side where the nerve cord is being formed (p. 280). 

 Those cells which are forming the new mesoderm presumably 

 derived from the primary mesoblasts in the embryonic develop- 

 ment (Wilson, '89 and '92)- also have very large nucleoli, 

 differing very little in appearance from the neoblasts in a re- 

 generating tail (Randolph, '92). In contrast to this, in the 

 older part of the worm, the nucleoli of the mesoderm and ecto- 

 derm cells are very small, in the case of the latter mere dots 

 under a magnification of 1,000 X. 



In regeneration, as already mentioned, the nucleoli of the 

 neoblasts and hypodermal cells become greatly enlarged. There 

 is also at this time an increase in the amount of nucleolar sub- 

 stance in the gut cells. For ten or eleven segments from the 

 wound, the nucleoli enlarge, a process followed by the appearance 

 of numerous instances of double nucleoli two within a single 

 nucleus (p. 285). 



This occurrence of double nucleoli is taken by Iwanow ('03) 

 and Krecker ('10) as evidence that amitosis is frequent in the 

 production of the new gut tissue. In Lumbriculus there is no 

 evidence of any division or even of a clearly defined constriction 

 in any of the nuclei of the gut which contain two nucleoli. The 

 individual nucleoli in the case of the double one are usually 

 smaller, and in no case larger, than those in the neighboring 

 cells where but a single nucleolus is present. It seems, then, 

 that the division of the nucleolar material into two parts is not 

 in preparation for a succeeding cell division. Rather as this 

 material accumulates it continues to exist in a single droplet 

 until it reaches a certain size and then divides. This splitting 

 into two parts may perhaps be due to the fact that a droplet 

 of material of its consistency and composition has a certain 



