234 ROBERT CHAMBERS AND HERBERT POLLACK. 



enclosing fertilization membrane. It is not until the eggs reach 

 the 32, 64 or even 128 celled stage that the blastomeres become 

 sufficiently adherent to form a comparatively intact wall about 

 the segmentation cavity. Dyes, injected before the cavity 

 becomes completely enclosed, immediately escape through the 

 gaps between the blastomeres. In later stages the injected dye 

 is retained for a longer period. The color of the dye, however, 

 always begins to fade within a minute or two after the injection 

 and in no case could an appreciable color be detected after 5 to 

 10 minutes. 



The stages injected included the coarse and fine celled blastulae, 

 early and late gastrulae, and Auriculariae of five and ten days 

 growth. In every case the colors of the indicators within the 

 blastocoele were identical with those of the indicators in the 

 environing sea water. 



Echinarachnius. The early blastomeres of the Echinarachnius 

 ovum are more adherent than those of the Asterias. In the two 

 and four celled stage the hyaline plasma layer is strong enough 

 to press the two blastomeres closely together (7). By inserting 

 micropipette through this layer and between the contiguous 

 blastomeres the injection of the dye solution creates a temporary 

 blastocoele. The blastocoele of early and late blastulae, gastrulae 

 and plutei were injected with the dyes. In every case the 

 colors assumed by the dyes were those typical for the pH of the 

 surrounding sea water. 



Dyes were also injected into the blastocoele of a pluteus 

 fifteen days old containing a young echinus-rudiment. The 

 dyes diffused through the blastocoele and into its prolongations 

 in the lips and arms of the pluteus. The color of the dye in the 

 blastocoele was always that of the dye in sea water and always 

 faded within a few minutes. 



In order to test the effect of changing the pH of the external 

 environment blastulse, gastrulae, and early and late plutei, 

 placed in a hanging drop of normal sea water, were injected 

 with dye solutions and were then transferred into acidified sea 

 water the pH of which was still consistent with viable conditions 

 (pH 6.6 ). The color in the blastocoeles changed within a few 

 seconds after immersion to correspond with the new pH. On 



