68 BULLETIN OF THE 



which any bud arises goes to form that bud ; but some of it is, appar- 

 ently, passed along under the highly metamorphosed cells of the ecto- 

 derm, again to divide itself, one part going to form a new polypide, the 

 other to form the Anlagen of new buds. In Gristatella, this embryonic 

 mass of cells of the inner layer of the bud seems to be to a considerable 

 extent independent of the highly metamorphosed ectoderm, and to form 

 at places a sort of third layer, lying below the true ectoderm and above 

 the muscularis with the coelomic epithelium. Here, too, Avhile it is 

 easy to see buds arise from preceding buds in the adult colony, we 

 cannot consider our question answered until we have discovered the 

 origin of the cells from which, as from a stolon, the Anlagen of polypides 

 successively arise. 



I desire to say that I have avoided giving a full account of the on- 

 togeny of these species, both because it is not directly required for the 

 solution of the problems in hand, and because we are promised studies 

 in this field by Braem. 



The eggs of Phylactolsemata arise, as has long been affirmed, from the 

 coelomic epithelium of the body wall. The evidence of this is conclusive, 

 for one often sees in a single section various stages in the development 

 of the eggs. (Plate XI. Fig. 93, ov'.) It is also to be observed that 

 they do not arise indiscriminately from any region of the body wall, but 

 always close to the neck of a polypide. Sooner or later these eggs, 

 surrounded it may be by a few follicular cells, are enclosed in an oa3cium, 

 and here undergo their development up to the stage of a young stock, 

 possessing perhaps a dozen immature polypides. In the figures on 

 Plates XL and XII. the ocecium (oce.) has been usually drawn, but in 

 Figures 100 and 104 it has been omitted. As a result of cleavage, a 

 blastula is formed, and from one pole of this — the pole nearest to the 

 neck of the ocecium — cells are given off which move into the blastococl 

 (Figs. 94, 98) and finally come to line the cavity. It is important to 

 observe that in the earliest stage of this process found there were four 

 inner cells, of which two are represented in the section (Fig. 94, rns'drm. 

 + en^drrn.). Thus the two layers of the adult body wall are established. 

 Up to this stage the conditions are practically the same in Gristatella 

 and Plumatella. From now on, they are somewhat different in the two 

 genera. 



The first difference to be noticed is in the ocecium itself. In Grista- 

 tella the cells composing this rapidly become a pavement epithelium 

 (Fig. 97) ; in Plumatella, on the contrary, the cells of the ocecium 

 remain columnar (Fig. 99). The neck of the ocecium also differs in the 



