the Freshwater Sponges. 409 



On dissecting larger portions of sponges, within which swarm- 

 spores exist, the latter are easily lacerated, and Iragmeuts only 

 of them become separated for examination, in which the ciliary 

 motion continues active. Dujardin was not aware of the origin 

 of these portions when he described the movements of the 

 sponges. It sometimes happens also, that the spermatozoa- 

 like bodies, hereafter described, adhere to a smooth piece of 

 sponge, which exhibits the Amoeba like movements, and that 

 they carry it about with them in the liquid. These bodies were 

 also unknow^n to Dujardin. 1 am unacquainted with the other 

 moveable forms of the sponges which Dujardin calls Monad- 

 like. 



Beneath the epithelial layer the cortical substance is situated, 

 the thickness of which is considerable in comparison with the 

 cellular layer — it is visible even to the naked eye. Even under 

 a high magnifying power, no definite structure could be detected 

 in it. It forms a gelatinous mass, in which here and there 

 some granules of fat are scattered, without regular arrangement. 

 AVhen isolated portions of sponge are separated by dissection, 

 so that they are unconnected with the cilia, they exhibit the 

 same locomotive phtenomena as the sponge-cells themselves. 



Next to the cortical substance comes the medullary portion, 

 which tills the interior of the spore as a spheroidal mass. Even 

 under a low magnifying power, this is seen to form a body 

 distinct from the cortical layer. The diameter of this spheroid 

 at its broadest part is about ^'^ inch ; but it varies in about the 

 same degree as tiie swarm-spore itself. Its surface consists of a 

 thinner mucoid layer, and the interior is the same portion of the 

 swarm-spore, which exhibits great varieties in different specimens, 

 whilst the remainder is nearly constant. The larger and most 

 anterior portion of the spheroid in the swarm-spores examined 

 early in June formed a pulpy mass, with fine scattered granules; 

 the posterior part of the spheroid exhibited larger and smaller 

 fat-like granules, forming with sarcoid matter larger and smaller 

 globules, which, when kept for some time in water, became con- 

 fluent. Many of them contained a very highly refractive body, 

 which sometimes almost entirely filled the gelatinous globule; 

 sometimes these bodies were found without any gelatinous enve- 

 lope, and were of about half the size of an ordinary sponge- 

 cell. The above-described contents give rise to the white ap- 

 pearance, visible with the naked eye, in the posterior part of the 

 swarm-spore. The entire spheroid, both the transparent and 

 the white portions, contains extremely small siliceous needles, 

 often of exactly the same shape as the adult spicula. The 

 smallest are of a barely measurable breadth, but about j-^j^-^ inch 

 in length ; the larger being about jj^ inch broad, and 7}^ and 



