lOO JOURNAL OF THE 



cells, are found in some larvae. Division of the cells then 

 ensues, and the hollow sphere gradually assumes the 

 nature of a flagellated chamber. In some larvae, on the 

 other hand, all the formative cells may break up into fine 

 cells before the marking out of any flagellated chambers. 

 The mesenchyme of such larvae consists of a solid mass of 

 fine cells, with here and there a formative cell. The flag- 

 ellated chambers of such a larva must be formed directly 

 from a group of fine cells, probably by some rearrangement 

 of the cells round a central cavity. In other larvae, both 

 processes go on at the same time. Some of the formative 

 cells arrange themselves in hollow spheres and form cham- 

 bers directly, others break up into solid masses of small 

 cells, which subsequently acquire a cavity. That a single 

 formative cell itself ever forms a chamber, I do not believe. 



In whichever way the flagellated chamber is formed, it 

 at first has no connection with the canals. It, like any 

 particular canal, is, in its origin, a lacuna, its cavity being 

 an intercellular space. 



In deciding phylogenetic questions, perhaps not much 

 weight should be attached to a development like this; but 

 whatever weight it has, is in favor of MetschnikofF's 

 theory of the solid ancestry of sponges. The solid swim- 

 ming larva itself, and the details of the metamorphosis 

 (the origin of the flagellated chambers, excurrent and 

 incurrent canals, and subdermal spaces, as independent 

 lacunae in a matrix of amoeboid cells) are all understood on 

 this theory. Conversely, if we hold to the view which 

 regards the calcareous sponges (Ascons) as the primitive 

 type, the development of Esperella may, of course, be 

 regarded as an extreme case of coenogeny. 



The development of Esperella, it seems to me, has per- 

 haps a bearing on problems out of the range of pure mor- 

 phology. Without discussing the matter in detail, I may 

 point out the striking resemblance between this asexual 



