228 Chas. W. and G. T. Hargitt. 



into the coelenteron where degeneration occurred. Hence Smith 

 conchides that ingression plays no part in the entoderm formation 

 of Aureha flavidula. 



A comparative study of several species of Aureha and of Cyanea 

 arctica was made by Hyde (1894) who found that the cleavage 

 might be regular or irregular, equal or unequal. The first and 

 second cleavage furrows were meridional, the third equatorial. 

 After the third division the cells were commonly smaller at one 

 pole. In all species a blastula was formed, the cavity usually 

 appearing first in eight or sixteen-cell stage. In A. marginalis 

 a real delamination of the blastula cells occurred and was multi- 

 polar in extent, in this resembling Lucernaria (Kowalevsky), the 

 inner cells formed an irregular layer and finally the prostoma 

 broke through. In A. flavidula an ingression of entire cells, or a 

 delamination, took place from different parts of the blastula wall 

 and the cells thus free in the cavity assembled at one pole. This 

 pole bent in to form a small funnel-shaped opening, the free cells 

 grouped themselves about this in a layer, and the gastrula was 

 formed. This is somewhat similar to the condition in A. aurita 

 (Goette), the entoderm being formed from a small portion of the in- 

 bent wall of the blastula and from the cells which had migrated 

 to this pole. A second method of gastrulation was found resem- 

 bling that described by Glaus (A. aurita) and Smith (A. flavidula), 

 viz., an invagination, though a few cells might migrate from the 

 wall and join with the invaginated cells. Hyde found that one of 

 the characteristics of the cells which wandered into the cleavage 

 cavity was that their nuclei were usually broken into small chro- 

 matin particles which were scattered through the cell, a condi- 

 tion noted earlier by Smith. In Cyanea arctica an invagination 

 took place, but there were added to the invaginated cells some 

 free cells arising by delamination from the blastula wall of the 

 invagination pole. No migration of cells occurred in Gyanea. 

 Thus in all three species Hyde finds a blastula with differentiated 

 poles and in the cleavage cavity, often, a coagulated liquid and 

 yolk grains. In the process of entoderm formation delamination 

 occurred alone or in conjunction with other processes : in A. margi- 

 nalis delamination alone; in Gyanea delamination limited to a 



