48 J. G. WALLER ON FRESH-WATER SPONGES. 



are familiar to us in many organisms in an adult and matured con- 

 dition. Here it is evidently not of that character, but is a stage of 

 growth belonging to the young sponge, which may fairly be pre- 

 sumed to have commenced from one or more ova. In the in- 

 stance here given, we have the sponge actually developed upon the 

 ovarian capsule, and in immediate proximity to the foramen, 

 through which the ova pass out, and was clearly in the earliest 

 stage of development. It appears to me that the phenomena 

 rather show an analogy to the encysted state observed in so many 

 of the lower organisms, and had a resemblance in its result to what 

 I witnessed in Actinophrys Sol.* This question I leave for others 

 to decide, and hope there may be amongst our friends those whose 

 experience may help us to a conclusion. 



Of the food of the Fresh-water Sponges we know but little, yet, 

 if we may judge from the abundance of diatomacese frequently seen 

 upon their tissues, they at least must fonn a part of it. The fol- 

 lowing is a list of those varieties I have found upon the membranes 

 and other portions of S. lacustris. 



Pleurosigma attenuata Cymbella gastroides 

 Navicula cuspidata „ cuspidata 



Meloseira nummuloides „ boekii 



Pinnul tria major Surirella biseriata 



Cocconeis transversalis Amphora ovalis 

 Campylodiscus spiralis „ membranacea 



Cymatopleura solea Encyonema prostratum, &c., &c. 

 ,, elliptica 



I must, however, mention that the sides of Hampton Lock, 

 whence my specimen was taken, are so rich in Diatomacese as to 

 look as if covered with treacle ; and it would, therefore, be rather 

 a marvel if we did not find some upon the membranes and other 

 parts of a sponge growing in that locality. 



* See Article on the Conjugation of Actinopliys Sol. 



