3OO LEONARD P. SAYLES. 



neoblasts. Evidence presented here (pp. 290 and 297) does not 

 support this idea but rather the view that a similar underlying 

 cause brings about the changes which occur in the metamorphosis 

 both of the neoblasts and of the ectoderm cells. During the 

 first two days of regeneration all the cells of the hypodermis in 

 the immediate vicinity of the wound develop large nuclei and 

 nucleoli. After this time the ones found dorsally and laterally 

 slow down whereas those in the ventral region continue to 

 enlarge. Neoblasts are rarely, if ever, found at the wound at 

 the time when the increase in size of the hypodermal cells becomes 

 apparent (between six and twelve hours after the cut). From 

 that time until the largest cells are formed the enlargement seems 

 to be a continuous process without any sudden change or increase 

 in rate which might be produced by the presence of neoblasts. 

 The fact that in posterior regeneration metamorphosed ectoderm 

 cells and neoblasts are always found very near one another is 

 cited by Krecker ('10) as proof that there is some relation 

 between them. This proximity of these two types of cells is 

 perhaps equally well explained if the reason for the presence of 

 each in the ventral region is considered. The cells of the ventral 

 hypodermis are transformed in the process of proliferation and 

 migration to form the nerve cord of the regenerating region. 

 The neoblasts migrate to the posterior end from the old tissue 

 along this same structure. These cells, then, are brought to- 

 gether not because one causes the modification of the other, but 

 rather from the fact that each type has a certain relation to the 

 nerve cord. The view that the same cause produces the changes 

 in the cells of both types seems to fulfill all the requirements 

 and to be a simpler explanation than that given by Krecker. 

 Furthermore, there is no apparent reason why the ectoderm, 

 any more than the endoderm, should need to be activated by 

 another type of cell. 



Function of the Nucleolus. 



Various theories have been advanced regarding the function of 

 the true nucleolus or plasmosome. Montgomery ('98) and 

 Ludford ('22) give a rather complete discussion of the work of 

 many investigators. The more recent results seem to indicate 



