No. 2. — The Gastrulation of Aurelia fiavidula, Per. <&; Les. 

 By Feakk Smith. ^ 



Preceding the appearance of Goette's ('87) publication in 1887 upon 

 the development of Aurelia aurita and Cotylorhiza tuberculata, the gas- 

 trulation of Aurelia had been regarded, in the light of the studies of 

 Kowalewsky, Haeckel, Claus, and others, as the result of invagination or 

 at least of a process nearer to invagination than to any other method of 

 gastrulation. 



Guette's work seemed to show, however, that, instead of an invagina- 

 tion, there is an ingression of cells to form the entoderm, and that the 

 first result of this ingression is the production of a solid gastrula, or 

 sterrogastrula, which is only subsequently hollowed out, and is put into 

 communication with the exterior through the formation of a prostoma 

 at a still later period. Recently, in a paper dealing especially with the 

 development of Cotylorhiza tuberculata, Claus ('90) reaffirms the posi- 

 tion taken in his previous paper ('83), in which the gastrulation in 

 Aurelia was represented as being simply a modification of invagination. 

 In recent papers by Hamann ('90) and McMurrich ('91), Goette's views 

 are adopted, and form part of the basis for statements that, in the devel- 

 opment of the Scyphomedusfe, invagination, instead of being the rule, is 

 the exception. 



This want of agreement among those who have given the subject 

 most attention makes the determination of the actual method of o-astru- 

 lation in Aurelia a matter of considerable interest, and it mav be 

 assumed that any contribution to the solution of the question will not 

 be unwelcome. 



Early in the current year, at the suggestion of Dr. E. L. Mark, I 

 undertook to investigate the method of gastrulation in A. flavidula. 



Through the kindness of Mr. B. H. Van Vleck of the Boston Society 

 of Natural History, I was enabled to spend two months of the summer 

 of 1887 at his seaside Laboratory at Annisquam, Mass., where I then 

 collected the material used in the present study. The embryos were 

 killed with picro-nitric acid, and preserved in 90 per cent alcohol, in 

 which they have been kept during the three intervening years. Of the 



^ Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of E. L. Mark, No. XXIX. 



VOL. XXII. — NO. 2. 



