464 



SCIENCE 



[N. S. Vol. XXXI. No. 795 



sets of fraternal twins, and of two sets of similar 

 children of separate birth, were shown in support 

 of the theory as stated. 

 Manufacture of the Squid Spermatophore : G. A. 



Drew, University of Maine. 

 Developmental Changes in Egg Substances: Ed- 

 win G. CoNKLiN, Princeton University. 

 In normal, living eggs of Physa, Limncea and 

 Planorbis two ooplasmic substances may be recog- 

 nized, a milliy or clear-gray substance, which 

 comes to the surface of the egg at the animal pole 

 at the time of the first maturation and which 

 then gradually spreads over the upper hemisphere, 

 and a yellow yolk-laden substance which is uni- 

 formly distributed through the egg before matura- 

 tion, but is confined to the vegetative hemisphere 

 after both maturation divisions. During the 

 cleavage the clear-gray substance goes into the 

 three quartets of ectomeres, the yellow material 

 into the entomeres and mesomeres. 



When eentrifuged with a force equal to 600 

 times gravity for from five to twenty minutes 

 these substances stratify in three zones, a gray 

 zone of light substance at the central pole, a 

 yellow zone of heavy substance at the distal pole, 

 and a zone of clear substance, containing the 

 nucleus, between these two. 



When eentrifuged before the first maturation 

 division the proportions of these three substances 

 are, gray one eighth, clear three eighths, yellow 

 one half. Centrifuged just before the first 

 cleavage, the gray and clear substances are not 

 distinctly separated and the proportions are, gray 

 and clear seven eighths, yellow one eighth. 



Before the first maturation the centrifuged eggs 

 orient rapidly with the yellow pole down and the 

 gray pole up ; after the maturation divisions these 

 same eggs orient very slowly, though the gray and 

 yellow substances remain distinct. Also eggs cen- 

 trifuged after the maturation divisions orient 

 very slowly. 



Before the first maturation the gray and clear 

 substances are finely granular, without the ap- 

 pearance of vacuoles or spherules, and the yellow 

 material is coarsely granular and contains yolk 

 spherules. After the maturation divisions the 

 gray and clear substances contain vacuoles or 

 spherules, and the yellow is apparently less 

 spherular than in the earlier period. 



Some of these changes may be due to the in- 

 creased viscosity of the ooplasm in the later stage 

 as compared with the earlier one, though this is 

 not the only factor involved, since the stratifica- 



tion is less complete in later stages even when 

 greater centrifugal force is used. In probably all 

 eases there is a redistribution, to a certain extent, 

 of the stratified substances during mitosis, but 

 this is never complete, and the original planes of 

 stratification may be observed for a long time 

 during the development. 



All eggs centrifuged before the first maturation 

 division develop normally; centrifuged during the 

 maturation divisions about one half develop nor- 

 mally, and one half abnormallj'; centrifuged at 

 the time of the first cleavage, or just before, 

 almost all develop abnormally. There is no evi- 

 dence that this result is due to greater injury to 

 the mitotic figure in the later stages than in the 

 earlier ones. Embryos, otherwise entirely normal, 

 may be produced in which the yellow and gray 

 substances may be distributed in any axis, and 

 even where the distribution of all the substances 

 to the cleavage cells is abnormal and unsymmet- 

 rical, normal development may result. 



Neither the yellow nor the gray substances are 

 formative, and neither are indispensable to devel- 

 opment. They may be distributed to the first four 

 cells in varying proportions and yet the resulting 

 development may be perfectly normal; either may 

 even be thrown entirely out of the egg and yet tlie 

 remainder may develop into a normal snail. The 

 gray substance is largely of a fatty nature, the 

 j-ellow contains yolk, and both may be regarded 

 as " inclusions " in the protoplasm. On the other 

 hand, the clear substance is indispensable to 

 development, though it may be formed anew in 

 cells which lack it if a nucleus is present, and 

 this clear substance in turn contributes to the 

 growth of the nucleus, whereas the other sub- 

 stances do not. Finally, the clear substance alone, 

 of all the ooplasmic substances, increases in quan- 

 tity during development. It is therefore true pro- 

 toplasm. Nevertheless, normal development may 

 result from eggs in which this substance is ab- 

 normally distributed as regards both polarity and 

 symmetry, and in this respect it does not cor- 

 respond to the " ground substance " of Lillie. 



The Fertilization Membrane of Nereis: Fbank R. 



Lillie, University of Chicago. 



In the unfertilized egg of the Heteronereis found 

 swarming at th^ surface of the water on moonless 

 summer evenings at Woods Hole, there occurs a 

 layer of coarsely alveolar protoplasm between the 

 vitelline membrane and the yolk-bearing proto- 

 plasm. This layer, which is 6-7 jj. in thickness 

 and entirely devoid of yolk, has been called the 



