1885.] NEW-YORK MICROSCOPICAL SOCIETY. 119 



the large cells are upon one side, or the basal half, and the small 

 cells occupy the other portion. The cell thus transformed is 

 then passed out of the body-wall of the sponge into the canal, 

 and is carried by the current of water which it there encounters, 

 into the central cavity of the sponge, and thence through the 

 osculum into the waters without. It is there moved about by 

 its cilia and by the sea-currents until, striking some hard object, 

 it anchors itself by its basal extremity. But, meanwhile, changes 

 have been going on within the egg itself. The two kinds of 

 cells have separated so as to produce a central or segmentation 

 cavity, with the cells arranged as a shell or coating around the 

 cavity — and the little animal forms what is known as a morula. 

 A collarette of cells is then formed around the centre of the 

 embryo, and by the multiplication of these and the other cells 

 the segmentation cavity becomes nearly or quite obliterated. 

 At the same time the ciliated cells of the outside of the embryo 

 grow upward all around it, and soon a gastrula is the result — or 

 a bottle-shaped animal with a central cavity which is lined with 

 ciliated cells and is in communication, by many pores, with the 

 waters without ; that is, we have a newly-formed sponge. 



The flagellate cells with which we observe the interior of our 

 newly-formed sponge to be lined — whence come they ? They are 

 simply the exoderm cells of the original egg transformed into 

 monads. Now, a monad is a Protozoon, since its growth does 

 not involve change in cell-structure. But the development of 

 the sponge does involve a process of differentation, and hence 

 this animal ought, I think, to be ranked as a Metazoon. 



I have spoken of the sponge as acommunity of animals. How 

 is that community formed ? Returning to our sponge, and watch- 

 ing it carefully, as before, we find one or more buds forming on 

 the outside. These do not begin as growths upon the exterior, 

 but as eversions of the wall itself, which appear, at first, as in- 

 dentations in the inner surface. Presently an opening is formed 

 at the apex of the bud. This becomes an osculum, resembling 

 that of the parent and performing the same function. These 

 buds start early, and grow with the growth of the parent, and 

 each bud becomes a centre from which other buds shall spring, 

 from each of which proceed yet other ramifications. Since the 

 original parent form, with the oldest buds or branches, grows a 

 little higher than the others, we shall have, as the result of the 



