53 



On Variation in Spongilla fluviatilis. 

 By J. G. Waller. 



(Read April 26th, 1878 J 

 Plate V. 



On a former occasion, I gave the result of some observations on 

 the two British freshwater sponges. My present remarks will be 

 confined to Spongilla fluviatilis. Dr. Bowerbank, in his admirable 

 work on the British Spongiadaa, the result of a long life of research, 

 makes the form of the spicule of the skeleton, membranes, &c, 

 one of the distinctions of species. It is not only convenient, but, 

 as an important part of the anatomy, a necessary item in the task of 

 classification. But a question arises to what extent this is to be 

 used : for the tendency to multiply species, though it has long 

 obtained amongst naturalists, presents a formidable barrier to the 

 student, in the large increase of terminologies, which, in their varied 

 combinations, seldom convey any idea to the mind. It is, however, 

 with some diffidence that I enter into so important a subject, and it 

 is not by any means to disparage the many eminent men, who have 

 done so much to advance our knowledge of natural history. But I 

 feel it is forced upon me, either to protest against the excess of this 

 practice, or to follow it myself. The latter I cannot do until the 

 question is settled, whether it may not be as easy to combine 

 under the title of " variation," instead of making a divergence under 

 the name of " species." 



In the third volume of the " British Spongiadee " Dr. Bower- 

 bank has introduced us to two new species of native Spongilla?. 

 Both were found in the river Exe, or reservoir in connection with it, 

 by Mr. Edw. Parfitt, of Exeter. One of these he has named S. 

 sceptrifera, on account of its membranes having a small spicule, 

 suggesting the sceptre-form character. One specimen of this only 

 having been found, and that without the ovaria, which usually dis- 

 tinguish the Spongilla, our knowledge of it is at present limited. 

 But the other nearly resembles, in all its characters, usual specimens 



