340 ROBERT CHAMBERS. 



The fluid interior of the mature unfertilized egg, if isolated by 

 being made to escape through a tear or the cortex, withstands dis- 

 integration for 24 to 36 hours. The presence of even a small part 

 of the original cortex in organic continuity with it causes it to 

 disintegrate in about the same time as an entire mature egg. This 

 would indicate that the reactions which make for disintegration 

 reside chiefly in the cortex. This, together with the fact that the 

 cortex of the egg is necessary for fertilization, would indicate that 

 the cortex is the seat of the initial activation processes of the egg. 

 The relatively inactive central material of the starfish and sa'nd- 

 dollar egg somewhat resembles that of the Linergcs, the Scy- 

 phomedusan, which Conklin ('08) has described. Conklin speaks 

 of "the large cavity in the line of the first cleavage furrow filled 

 with gelatinous or fluid substance, which forms the ground sub- 

 stance of the central area of the unsegmented egg." He found 

 that most of the ground substance escapes into the cleavage cav- 

 ity and suggested that it is the fluid yoke which is gradually used 

 up in the nourishment of the embryo. The central substance of 

 the Llnerges egg is probably not strictly analogous with that of 

 the starfish or sand-dollar egg. In Linergcs cleavage is of a type 

 peculiar to yolk-laden eggs and the central substance escapes 

 during the first cleavage. On the other hand, in the echinoderm 

 egg the nucleus lies well within the central substance of the egg 

 and, upon fertilization, all of the endoplasm is used up in the 

 formation of the cleavage asters and nothing apparently escapes 

 into the early cleavage cavity. We can not, therefore, con- 

 clude that the interior of the Echinoderm egg consists of entirely 

 inert material. It lacks certain essential features, but when co- 

 existent with the cortex it plays a full part in the cleavage of 

 the egg. 



7. THE LOCALIZATION OF A SUBSTANCE WHICH RENDERS A STAR- 

 FISH EGG FERTILIZABLE. 



Wilson ('03"") in Cercbratulus and Rcnllla and Yatsu ('04 

 and '08) in Cerebratulns have shown that non-nucleated frag- 

 ments of the egg are capable of fertilization only after the ger- 

 minal vesicle has broken down. With more delicate methods 



