60 J. G. WALLER ON VARIATION 



There is always a tolerably quick current passing through." Now 

 this statement has some value, as Mr. Carter, in his article on the 

 Spongilla of the Exe, has hinted an opinion that the agitation of the 

 water might be a cause for the spinous condition of the spicule. I 

 must confess this was an idea also of mine, and I was watching to 

 see if this rule could be borne out. Obviously it cannot, for a mill- 

 stream is always agitated, and must be always strong in the vicinity 

 of the wheel. So as this specimen conforms to the type Sp.jiuviatilis 

 in general character, and having but the smooth spicule, under 

 such conditions we are not yet in a position to declare the law which 

 operates to produce the changes alluded to. 



Of all the examples of the freshwater sponge I have ever received, 

 this was the richest in sarcode. It was the very alderman of sponges, 

 fat to a degree, evidently enjoying life, and in full possession of that 

 by which life is sustained. The constant flow of the mill-stream 

 suited its constitution. Laying it out to dry in a summer's day, 

 the olfactory nerves soon became unpleasantly admonished. I 

 observed the blow-fly paying it assiduous attention, and in a few 

 days it was as full of maggots as a dead dog festering in a ditch. 

 The larvae were of two kinds — one a very common form, the other 

 having numerous feet, and the sponge was also full of eggs. Such a 

 phenomenon I had never seen before, and if there now could be a doubt 

 on the animality of the sponge, this fact may come into the argument. 



It abounded in ovaria, often packed closely together, even in this 

 declaring its pre-eminence. The birotulate spicules, however, were 

 long in the shaft ; in this not conforming to the type whose exact 

 character seems to elude my enquiry. (Fig. 5.) 



It is time now to generalize and draw deductions suggested by 

 the foregoing observations. I think I have sufficiently shown that 

 Sp.jiuviatilis is subject to considerable variation, consequent upon 

 some law as yet unknown to us. But, from the easy manner in 

 which the changes seem to pass through a series of gradations to a 

 complete development of parts, I cannot but feel it contrary, not 

 only to the interests of science, but to the facts arrayed before you, 

 to declare any one of these a new species. The differences between 

 the two extremes are certainly remarkable when they are brought 

 together, and require some classification, but surely we should not 

 want to travel to the Bombay tanks to find a name for a sponge 

 found in an English river ; still less to baptize it with the name of 

 a German naturalist, and that of its discoverer tacked on. 



