MUSEUM OF COMPARATIVE ZOOLOGY. 128 
subject to slight individual variations, but the number of such cells is 
nevertheless in quite close correlation with the stage of development. An 
examination of Goette’s Figures 6-9 (’87, Taf. I.) reveals such a simi- 
larity in the number and size of the cells composing the ectoderm in each 
of the four supposed stages, that I am driven to the conclusion that 
they represent sections from specimens of a single stage of development, 
which may have been produced by cutting in planes having different 
relations to the chief axis of the embryo. 
When we consider that in the majority of embryos there are no signs 
of ingression, and that in the cases where it does occur the immigrating 
cells in some instances degenerate early, and in others persist undivided 
throughout the process of gastrulation, and that they at no time show evi- 
dences of even sharing in the formation of an entoderm, — and when we 
further reflect that all the conditions shown in Goette’s Figures 6-9 can 
easily be reproduced from sections of invaginating gastrule of a single 
stage of development, — it seems improbable that the entoderm of Au- 
relia develops even occasionally by ingression, At present, therefore, 
there seems to me to be no evidence that in this genus gastrulation 
occurs by both methods, invagination and ingression. 
The Scyphomedus® present several interesting variations in gastru- 
lation. The anomalous development occurring in Lucernaria is as far 
removed from the usual process as that group itself is from the other 
Seyphomedusw. According to MeMurrich (’91, p. 314), the solid plan- 
ula in Cyanea arctica is formed by the immigration of certain of the 
blastula cells. This planula is subsequently hollowed out, and gives 
rise to a structure like an invaginate gastrula, but it is formed without 
any invagination. In Cyanea capillata (Hamann, ’90, pp. 16, 17) there 
seems to be a solid ingrowth of cells from one pole of the embryo, and a 
simultaneous development of the cwlenteron. The entoderm of Chry- 
saora (Claus, ’83, p. 5, Taf. I. Fig. 21 4) is developed in away which is 
somewhat similar to that described by Hamann for Cyanea capillata, 
According to Claus (’83, p. 2, and ’90, p. 4), the gastrulation of Aurelia 
aurita approximates the method by invagination a little more closely 
than that of Chrysaora, since its cells are arranged in a single layer 
about the fissure-like coolenteron. Aurelia flavidula exhibits a still more 
nearly typical invagination, since the coolenteron is from the beginning 
an open sac-like cavity. Cotylorhiza tuberculata (Cassiopea Borbonica) 
has an invaginate gastrula which closely resembles that of Aurelia 
flavidula (Glaus, ’90, Taf. I. Figs, 2 and 3; Kowalevsky, ’73, Taf. II. 
Fig. 1). Finally, in Pelagia noctiluca and Nansithoé marginata, as 
