EMBRYOLOGY OF CRYPTOBRANCHUS 117 



outer side in part accounts for the greater concentration of nucleoli 

 on this side, but it is inadequate to account for all of it; moreover 

 the axis of excentricity in form due to shrinkage does not always 

 correspond accurately to the axis of excentricity in the arrange- 

 ment of the nucleoli. 



This excentric distribution of material marks an axis which 

 corresponds, roughly at least, to the polar axis at the time of 

 maturation; the nucleoli accumulate on the side which is to become 

 the animal pole, and thus perhaps afford a second indication of 

 polarity. King ('08) found this condition in Buf o at the time when 

 the nucleus was moving from the center of the egg to the animal 

 pole, and suggested the possibility that the accumulation of most 

 of the nucleoli in one part of the nucleus might have something to 

 do with this movement. In Cryptobranchus this concentration 

 of the nucleoli begins long before the migration of the germinal 

 vesicle to the surface, and indeed before the formation of any 

 yolk; it is most marked in the advanced ovocytes of a 35 cm. 

 female, when the yolk is just beginning to form. As will appear 

 from the study of later stages, this arrangement of the nucleoli 

 does not persist during the actual migration of the germinal vesi- 

 cle; nevertheless the early occurrence of axial concentration of 

 nucleoli is significant. 



In the ovary of a 35 cm. female, we find that occasionally, 

 through the folding of the ovarian wall, an ovocyte has been 

 thrust deep into the central cavity and has come in contact with 

 the nutrient ovarian wall of the opposite side. The side opposite 

 the stalk of the follicle now becomes the side best nourished, and 

 here the nucleoli accumulate. Thus nature's experiment shows 

 that the accumulation of nucleoli, and perhaps polarity, is not 

 something predetermined in the egg, or even fixed by the relation 

 of the egg to the ovarian wall within which it develops, but is 

 a phenomenon depending upon larger environmental relations 

 which probably have to do with nutrition; for as a consequence 

 of the changed position of the egg the nucleoli accumulate on the 

 opposite side from that favored by the original environment. 



In the ovocytes of immature females with body lengths of from 

 35 to 38 cm., the yolk first appears in a narrow zone near the periph- 



