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



constitute more than 6 or 7 per cent, of its skeleton, and it is 

 somewhat shorter than the others. The next point of dissimi- 

 larity between them is in the structure of the ovaria, so far as re- 

 gards the sjDicula of the integument. 



The bi-rotulate form of S. Jluviatilis must be known to every 

 microscopist, as it is so frequently figured in works on the Micro- 

 scope. Those of S. lacustris are totally different, being similar in 

 character, though smaller, to those of its membranes, but varying 

 in their curvatures to such an extent that I have occasionally seen 

 them taking that of a complete circle. The preparation of the 

 ovaria showing the spicula is extremely easy. There is no 

 necessity for any boiling in nitric acid, as recommended by Dr. 

 Bowerbank, but a section of the sponge containing them needs only 

 to be steeped in strong spirits of turpentine for a few days, and 

 then mounted in balsam to show their structure completely, and it 

 is the more interesting as they are seen in situ. 



There is another characteristic of the latter sponge which ob- 

 servers have not failed to note, i. e., the numerous abnormal forms 

 of spiculum which are found in it. But, indeed, they are quite as 

 numerous in S. Jluviatilis, and they are so far worth our notice 

 when they seem to play into shapes, which in other sponges are 

 constant. But I will now pass from these somewhat dry details to 

 matters of more interest. 



In the early part of November, 1870, accompanied by a friend, 

 I went into Hampton Lock, in search of the Fresh-water Sponges, 

 and returned home laden with a rich gathering of, as I thought, 

 both species. But it entirely consisted of S. Jluviatilis, the lobular 

 form of which deceived me, as I took it to be S. lacustris. On 

 reaching home and submitting a portion to examination, I found it 

 was pouring out a yelky substance of a dirty white colour, which 

 proved to consist of myriads of ova. These had a tendency to 

 aggregate together in masses upon the slide, perhaps by the law of 

 attraction, but in some cases these masses immediately threw out a 

 membranous projection like the pseudopodia of the Amoeba, which 

 they closely resembled ; and I regret that I was not able just 

 then, for want of leisure, to follow up any subsequent development. 

 After setting aside some pieces of the sponge as specimens, a few 

 fragments were left in the gathering bottle. This soon became 

 exceedingly offensive and perfectly black with decomj)Osition. In 

 a few days, however, purification ensued in the usual manner ; I 



