The Development of Scyphomedusse. 229 



few cells at the pole where the invagination occurs, invagination 

 being the chief process. In A. flavidula some blastula cells delami- 

 nate and some entire cells migrate into the cavity and these join 

 a small invagination; or a large invagination occurs and this is 

 only sometimes helped out by a few delaminated or migrated 

 cells. 



Hein's (1900) work upon Aurelia aurita gave results differing 

 from those of Goette, Smith, Hyde, and others, in that he found 

 it impossible to distinguish animal and vegetal poles because of 

 the similarity of the cells of the blastula. He agrees with Glaus 

 and Smith that from different regions of the blastula wall a few 

 cells may migrate inward, but these never take part in entoderm 

 formation, degenerating sooner or later. He found also an oc- 

 casional migration of entoderm cells into the coelenteron where 

 they degenerated. An invagination, with a rapid division of the 

 invaginated cells, led to the formation of the entoderm, the blas- 

 topore persisting as a very fine canal between the archenteron 

 and the outside. 



Goette (1900), in a short response to Hein's work, upheld the 

 work of Hyde in all particulars, and though he acknowledged that 

 invagination was the method of gastrulation in some cases, he 

 still maintained the view that ingression plays a more prominent 

 and active part among Scyphomedusse. He discards entirely the 

 view of Smith and Hein that the immigrated cells degenerate and 

 take no part in entoderm formation. 



C. W. Hargitt (1902a, 1902b) found that in Cyanea arctica 

 the early cleavage stages were passed while within the gastric 

 cavity or in the folds of the manubrium. Cleavage was total and 

 regular, a typical blastula formed which by invagination gave rise 

 to the gastrula. 



Continuing his investigations upon Scyphomedusa, Hein in 

 1903 presented the results of work upon Cotylorhiza tuberculata. 

 He found (as in Aurelia aurita) that a few cells ixdgrated from the 

 blastula wall into the blastocoel, but there they always degen- 

 erated. Gastrulation was by invagination, as he found in Aurelia 

 aurita, but in Cotylorhiza the blastopore soon closed while in Au- 

 relia it remained to form the prostoma. In neither species was 



