22 Mr. H. J. Cai'ter on the Ultimate Structure of SpoDgilla. 



of development the spherical, which we shall heuceforth call 

 "ovi-bearing," cells are polymorphic — identical, but for the 

 ovules, with the ordinary sponge-cell, — and surrounded by a 

 layer of peculiar cells equally polymorphic, which I have conjec- 

 tured to be the chief agents engaged in constructing the cap- 

 sule*. It is desirable also to remember that there are these two 

 kinds of cells in the composition of the seed-like body, because 

 we shall find by and bye that they appear in corresponding parts 

 of the newly developed Spungilla. Lastly, the seed-like body 

 presents a hole, which we shall call the " hilum." 



Having thus briefly alluded to the constituent parts of the 

 seed-like body, let us now pursue the development of Spongilla 

 from it. This takes place in the following order: viz. 1st. The 

 contents issue through the hilum under the form of a gelatinous 

 mass, in which the ovi-bearing cells and their contents appear 

 to be imbedded entire. 2ndly. The spicules begin to be deve- 

 loped, and with them is formed a delicate pellicle, which not 

 onl}'^ encloses the new Spongilla, but also the seed-like body : 

 to this pellicle we shall give the name of "investing membrane;" 

 this becomes separated by an interval (which we shall designate 

 the "cavity" of the investing membrane) from the gelatinous 

 mass containing the ovi-bearing cells, which we shall term the 

 "parenchyma." 3rdly. Apertures are developed in the investing 

 membrane, and a system of aflferent and efferent canals in the 

 parenchyma; the afferent canals commencing in many large 

 apertures and afterwards communicating with each other, and 

 the efferent canals commencing in ramusculi which end in a 

 single tubular vent. In this period also the spicular structure 

 is formed and arranged. 4thly. The ovi-bearing cells are deve- 

 loped into spherical ampullaceous sacs, communicating with the 

 afferent canals ; and the afferent and efferent currents are esta- 

 blished. We will now follow this more in detail. 



First Period. — Three or four days after the seed-like body 

 (which has never been allowed to get dryf) has been placed in 

 clear water, a white substance like cotton is seen to have issued 

 from the lower part of it. This, when examined, is found to 

 present a flat, transparent border, so abounding in (indolently 

 contracting) vesicles of different sizes, that it looks like an areolar 

 structure. I wish particularly to call attention to this point, 



* Annals, vol. xviii. pi. 6. figs. 41, 42. 



t For this purpose it is best to place a piece of Spongilla, charged with 

 the seed-like bodies, iu a basin of water, where it will soon get putrid ; but 

 this does not matter : the seed-like bodies still retain their vitality, and will 

 throw out the young Spongilla much more quickly than if taken fresh 

 from the living mass. Those which I have used for these experiments 

 belong to Spongilla alba, H. J. C, which was taken from the tank a vear 

 since. 



