518 WILSON. [Vol. V. 



course as in Esperella. The early stages in the formation of 

 the gemmule, owing to the extremely small size of the cells, 

 cannot be followed with the same accuracy as in Esperella, but 

 the process can be seen to be essentially the same. The " seg- 

 mentation," or gradual dissolution of the gemmule into its constit- 

 uent cells, takes place in the same way. The swimming larva 

 is, except in a few details, like the larva of Esperella, and the 

 metamorphosis takes place on the same lines. 



In the egg development of Tedanione, there is a total seg- 

 mentation, resulting in the formation of a solid morula. The 

 larva, when set free, is a solid oval body, completely covered 

 with a layer of columnar ciliated cells. The metamorphosis 

 was not observed. The segmentation of Hircinia is likewise 

 a total segmentation, resulting in the formation of a solid moru- 

 la. The development of the ovarian egg in these two forms is 

 essentially alike. The follicle during the growth of the egg is 

 surrounded by a large number of comparatively densely packed 

 mesenchyme cells, the duty of which is presumably to bring 

 nourishment to the growing egg (compare Fiedler's account 

 for Spongilla). The nucleus of the very young egg contains 

 a single large nucleolus more or less centrally placed. While 

 the egg is comparatively small, before it has reached more than 

 one-half its ultimate size, two small spherical masses of densely 

 staining chromatin are found adhering to opposite sides of 

 the inner face of the nuclear wall. As a rule, in eggs which 

 have reached the full size, only one or neither of these chroma- 

 tine balls is present. 



Occasionally, however, an egg is found of the full size and 

 still with both of the chromatin balls. One of the masses 

 is probably lost (thrown out ? ) at about the time when the 

 increase in size is completed. The remaining mass is thrown 

 out of the nucleus, and may sometimes be observed lying in the 

 egg yolk near the nucleus. The nucleus of the ripe egg thus 

 left without chromatin mass, is a poorly denned body in which 

 neither nuclear membrane nor chromatin is visible. The 

 maturation of the egg in these two sponges is seen to be very 

 like that of Spongilla, as described by Fiedler. 5 Fiedler regards 

 the two chromatin balls as polar bodies ; but as an objection to 

 this view it must be urged that they are formed (though not 

 discharged) long before the egg has reached its full size. 



