Hyatt.] 12 [November 1, 



P. Kennard, Miss Mary E. Rice, Miss M. L. Tinker, Miss E. 

 O. Patch, Miss Emma A. Temple, Miss Harriet E. Caryl, 

 Miss Laura B. White, Miss Jenny M. Arms, Miss R. E. Cole, 

 Miss Catherine J. Ireland, Mrs. J. W. Wolcott. 



Prof. A. Hyatt gave a full account of what had been done 

 upon the embryology of Sponges, and the views of different 

 writers, supplemented by observations of his own, upon the 

 earlier stages of several species. 



His own and Barrois' observations substantially agreed in denying 

 the existence of any gastrula stage in the siliceous, or in the kera- 

 tose sponges. The egg, in passing through the morula stage, is 

 either hollow, or develops an endoderm by delamination from the 

 ectoderm. In most siliceous sponges the egg in the first stages of 

 division is solid, but becomes hollow subsequently. A granular mass, 

 however, accumulates in the interior during the later stages of the 

 morula form in many species, which eventually fills the cavity, so 

 that the larva again becomes solid. During the morula stage, too, it 

 very frequently happens in the siliceous sponges that the egg is open 

 at one pole, but closed at the other. This may, of course, be due 

 entirely to the effect of contraction after death, but the structure 

 which permits this at one pole and not at another, is probably of 

 more importance. The unopened pole is closed by a large cell, and 

 the open pole has no such plug. The division of such eggs appears 

 to begin with three cells, but this is probably not the first stage, though 

 the first observed by the speaker in several Halichondrida. There 

 were in these forms only a single cell at one end of the oblong form 

 of the larva, and two, side by side, at the other. The single cell 

 appears to remain without division, though this was not directly 

 observed, and serves to prevent the opening from occurring at this 

 pole, whereas it may, and does, frequently occur by the separation 

 of the cells, at the other pole. It is at this open pole that the en- 

 larged cells afterwards occur, constituting the endoderm of Barrois, 

 and eventually in nearly all the types of keratose and siliceous sponges 

 form a sort of collar, which can be appropriately called the basal col- 

 lar. Whether the polar opening persists, or is an essential character- 

 istic in the larva from the morula stage until this period, Prof. Hyatt 

 could not say, not having been able to follow it closely; but it is proba- 

 ble that this is the fact, since the space in the centre of the collar is 



