64 FRANK R. LILLIE. 



ration spindle is attached to the surface, and may thus be sepa- 

 rated off in the yolk-bearing end of the centrifuged egg, if it lies 

 in a distal direction in the centrifuge and is not torn loose from 

 its attachment before rupture of the egg takes place. But while 

 the majority of large hyaline pieces contain the maturation 

 spindle and form polar bodies after fertilization, this happens 

 very rarely indeed in yolk-bearing pieces. 



I was interested to determine if the cleavage of the hyaline 

 pieces was unequal, and, if so, whether or not the proportions of 

 the cells approximated the normal. This is indeed the case ; in 

 most pieces taken before fertilization, that segment, the segmenta- 

 tion is unequal and in substantially the normal proportions. See- 

 ing that the inequality of cleavage of the normal egg is an unfailing 

 index of bilaterality, the same phenomenon in the parts must be 

 interpreted in the same way. 



The unequal cleavage of such hyaline parts absolutely devoid 

 of yolk is a most striking phenomenon. There is great variation 

 in the absolute size of such parts, but the cleavage remains pro- 

 portional. 



The parts vary not only in size, but also in the regions of the 

 egg that they represent. The latter conclusion obviously follows 

 from the fact that the direction of the centrifugal force is a matter 

 of chance. 



To show the strong tendency of pieces of the hyaline band 

 to segment in normal proportions the following result may be 

 cited. In experiment 10 F, August 18, 1908, a quantity of eggs 

 taken from the female at 10 A. M. was allowed to stand in sea 

 water without fertilization until 10 -.40 A. M. They were then 

 centrifuged about 7,500 revolutions in one minute with a radius 

 of 6 cm. and were thus broken up. The material was fertilized 

 at 10:43 and allowed to develop to the two-celled stage, then 

 fixed, stained and mounted entire in balsam. The impression of 

 the preparation is that in practically every segmented hyaline 

 piece the proportions of the cells are approximately normal. To 

 remove the personal equation as far as possible, I marked a ring 

 on the cover slip, and drew every segmented hyaline piece in it. 

 Of 26 pieces so drawn, none had divided equally ; in four pieces 

 of the 26 the small cell was proportionally larger than normal, 



