580 Chas. W. Hargitt 



discharge of the eggs from the summit of the gonophore. As a rule 

 it seems to be remarkably regulär and equal, a condition probably 

 facilitated by the essentially free and independent disposition of the 

 eggs about the conica! apex of the gonophore. While during the 

 earlier phases of cleavage the entire egg appears to be involved, 

 in some specimens there appears to be a condition of independent 

 nuclear proliferation similar to that found in many species of Tubu- 

 laria, among which that cited in a previous section of this paper 

 is an instance. Cleavage tìnally results in the formation of a solid 

 morula, or in some cases a morula-like embryo having something 

 of a syncytial character, it being impossible to distinguish any de- 

 tinite cellular Organization, but rather a multinucleate embryo, such 

 as is well known among not a few Hydromedusae. 



Formation of the Germ Layers. 



Concerning the ectoderm attention has already been directed 

 to its appearance at a comparatively early period in development. 

 Fig. 31 is one from an embryo which has just begun to assume the 

 piriform shape of the planula. In this it is as yet barely possible 

 to clearly distinguish the columnar shape of typical ectoderm cells 

 of an embryo at this stage. The ectoderma! nuclei are definite and 

 large, and for the most part snperficially disposed. At a somewhat 

 later period the ectoderm becomes finally and defiuitely differcntiated, 

 and the entire embryo more planula-like, apparently approaching 

 birth. Stili I bave not found any intrinsic diUerentiation among the 

 ectoderm cells themselves, such, for instance, as nematocysts. 



Concerning entoderm formation I am unable to specify. The 

 entodermal mass shown in Fig. 31 continues essentially unchanged, 

 probably up to and beyond the time of the birth of the planula, a 

 condition not uncommon among Hydromedusae generally. The 

 nuclei continue to proliferate, but without corresponding cytoplasmic 

 activity, at least during the distinctively embryouic development. 

 Differentiation of the entoderm probably takes place by a graduai 

 process of cellular Organization of the entodermal mass, parts of 

 which undoubtedly serve, as in other well-known cases, as nutritive 

 substance tili the larva finally attaches itself and assumes the polyp 

 stage, while the cellular Clements become organized into a defini- 

 tive entoderm. 



