the Freshwater Sponges. 41 1 



the base. In the same parts I have also found ciliated swarm- 

 spores; they lie completely in the mass of the living sponge, 

 but can seldom be separated from it uninjured. Empty shells 

 of gemmules are not found in these parts. The swarm- spores, 

 however, attach themselves firmly to the empty siliceous skele- 

 tons ; when detached, they swim about as usual. The aggre- 

 gated germ-granules seldom contain the small, smooth, and 

 spinous spicula in their interior ; but these are often found in 

 their immediate neighbourhood. The mucous envelope is some- 

 times separable, by evacuating the contents with gentle pressure ; 

 but it is structureless. The size of the aggregations of germ- 

 granules varies from j^j to j^^ inch. The germ-granules are either 

 uniformly diffused through the entire substance, or are arranged 

 in spherical heaps, and mixed with fatty globules and mucous 

 matter. Many of them exhibit a distinct gelatinous globule, 

 which sometimes contains small fatty granules, at others also a 

 nucleus-like body. 



We may here recur to Carter^s investigations. As far as I 

 can conclude from his descriptions, the insular groups of germs, 

 which, according to Carter, pass into the variously shaped cells, 

 are my aggregations of germ-granules. But the statement of 

 this observer, that these escape directly from the gemmules, is 

 essentially different from my view. Were we to suppose that 

 Carter had directly observed this occurrence, and that it was 

 not simply based upon supposition, and that the swarm-spores 

 were absent in the sponges examined by him, the difference 

 between the developments of such nearly allied formations would 

 be so great, that it could scarcely occur. In some instances I 

 saw pieces of sponge, the aggregations of germ-granules of 

 which had no longer the definite form, but appeared to be 

 undergoing decomposition. The mucous envelope was also 

 absent, the separate granules being scattered around them. 



Moreover, at the period at which all the above-described bodies 

 are present, large masses of sponge are always met with which 

 contain no trace of them. Even in one and the same locality, 

 we find near together Spongillse containing large numbers of 

 gemmules, swarm-spores, and aggregations of germ-granules, 

 and others in which none of these are present. 



Immature forms of the gelatinous substance and of the spicula. 

 — As early as June, white spots about the size of one or several 

 of the aggregations of germ -granules are perceptible on various 

 parts of the sponge, some of which are well defined, whilst others 

 are confluent with the surrounding parts. They are sometimes 

 also found upon other bodies at the bottom of the water, as 

 upon shells of the Mollusca, the exuviae of the larvse of the 

 Phryganida, upon straws, stones, and other similar objects upon 



