Seed-like Body of Spongilla. 99 



do not any of them present it ; while its occurrence in every 

 specimen of Grantia compressa already becoming effete under 

 the circumstances, seems to point out that, like the inflorescence 

 of plants, this state in sponges also occurs and goes at certain 

 periods, and its elements are in vain sought for before or after 

 these periods in any individual of the same species. 



Having now become acquainted with the ovum of the marine 

 sponges, and its development from the egg-like form to the 

 embryo (for it is probable that in all it is more or less alike), 

 it appears to me evident that each spherical cell of the seed- 

 like body is also a distinct ovum ; but its development from 

 the seed-like body in the midst of the intercellular substance, 

 where it has to remain, somewhat differs from that of its 

 comparatively isolated condition in the marine sponges, where 

 it has to seek an object for itself to settle down and grow upon. ' 



Thus in the former it requires no crust of ectodermal mono- 

 ciliated cells for locomotion, nor does it require the endodermal 

 cells for further increase ; but the ovum and its capsular' 

 granules at once pass into a pavement of monociliated 

 spongozoa, which arrange themselves in the form of the 

 ampullaceous sac, in the midst of the intercellular substance 

 (see figure in the ' Annals,' to which I have first referred). As 

 this is going on, the pores and the branched excretory canal- 

 system are formed, which become respectively connected with 

 the two apertures of the ampullaceous sac. But whether this 

 takes places synchronously, or the cavities of the ampullaceous 

 sacs respectively push themselves through the intercellular 

 sarcode, and, as regards the latter, like streams of water, at last 

 all join together in one common excretory canal, is unknown 

 to me. (For the further development of the young Spongilla 

 from the seed-like body see my paper entitled " Ultimate 

 Structure of Spongilla" i Annals,' 1857, ser. 2. vol. xx. p. 21, 



P L1 ;) . 



Viewing the seed-like body, then, as a capsule filled with 

 ova, which issue from its hiliform opening and thus become de- 

 veloped en masse into the young Spongilla, it may be a question 

 whether the entire body may not be the ovarium of a spongo- 

 zoon in the first place, while, as in hundreds of instances of 

 the same kind in the animal kingdom, all the other parts have 

 perished, their functions having ended when sufficient nutri- 

 ment had been gathered and assimilated to support the 

 reproductive elements until they could do this for themselves. 



But, although this "question" of the origin of the seed-like 

 body remains to be answered, the object of the process seems 

 to derive explanation from the fact that the freshwater 

 sponges are, from their habitat, exposed to variable periods of 



7* 



