224 



lip has appeared, as in the diagram of a side view of a compressed 

 egg, given in Fig. 15, the effect of this tendency is to cause the 

 dorsal lip (d. I) to move across the field in direction of the outer 

 arrow a. This may be demonstrated at any time by slackening the 

 rubber bands, which hold together the compressing plates — at once 

 a comparatively rapid rotation, in the direction mentioned, begins. If 

 the egg is strongly compressed, the rotation is slow, though it is 

 usually sufficient to materially affect the appa- 

 /cl.f rent position of the blastopore (position in 

 the microscopic image of the egg) — I have 

 observed eggs, however, in which for a time 

 no rotation was perceptible. The slow rotation 

 may be proved by measuring at intervals the 

 Fig i5_ distance of the ventral and dorsal lips (in the 



microscopic image) from their respective near 

 egg-edges, in an egg in which the ventral lip is observed to be 

 moving over the yolk (i. e. covering up yolk cells). In a tjqjical 

 case, the impression is given that the ventral lip remains nearly 

 stationary, while the dorsal lip travels across the yolk; but the fact 

 that the ventral lip is seen to cover up yolk cell after yolk cell, 

 shows that this lip is far from stationary — the only conclusion 

 possible is that the egg is rotating. 



Possibility of other interpretations of the obser- 

 vations on compressed and inverted eggs. Besides the 

 interpretation which I have put on my observations upon these eggs, 

 there are two others which are possible. 1. The ventral lip may be 

 stationary, the dorsal lip active, as is assumed in the Roux-Hertwig- 

 MoRGAN theoi-y. The apparent overgrowth by the ventral lip must 

 then be explained as due to a rotation of the whole yolk mass in 

 the direction of the inner arrow c in Fig. 15. It is very improbable 

 that any such rotation occures-as far as I know, no observer main- 

 tains its occurrence in the normal egg. 2. Or the dorsal lip may 

 be stationary, while the ventral lij) actively overgrows the yolk, and 

 the yolk itself is invaginated beneath the dorsal lip, in the direction 

 of the inner arrow b in Fig. 15, as is believed to be the case in 

 the normal egg by Sghultze ('90) and Kopsch ('95) — on what 

 seems to me insufficient evidence. With respect to this interpretation, 

 I must say that none of my observations on inverted eggs absolutely 

 contradict it. The results of my numerous pricking experiments, 

 however, lead me to believe that in the normally placed egg, the dorsal 

 lip is not stationary, but that both dorsal and ventral lips move across 



