Studies on Sponges. 



Dr. G. C. J. Tosmaer, 



Assistant at the Zoological Station. Naples. 



n. On the supposed difference between Lencandra 

 crambessa H. and aspera (0. S.) H., with an attempt 



to explain it. 



With Platea 28 and 29. 



Haeckel described in bis well-known Monograpli * two species of 

 Ms genus Leucandra^ which show however, as I hope to prove, so many 

 transitions that there can be little doubt that both are but varieties. A 

 glance on Haeckel's figures of L. aspera (0. S.) H. and L. cramhessa 

 H. compared with bis descriptions makes one think that both species 

 are easily to be distinguished one from another. But if one sees a great 

 quantity of specimens, it becomes clear that it is often not so easy to 

 determine them. Haeckel has known this too, as he (1. c. IL p. 182) 

 remarks that there are what he calls » transitorische Varietäten « from 

 L. cramhessa H. to L. aspera (0. S.) H. I never understood these tran- 

 sitory varieties. If two species vary so strongly as to show forms which 

 are between the two, this fact proves that they are what we call varie- 

 ties of one species : and we do not want the new idea of transitory va- 

 rieties. Every body now is convinced that species are not Constant, and 

 that it is difficult in many cases at least to circumscribe them. In fact 

 we only give specific names for our own practical use, because Nature 

 never makes such sharp distinctions . But if this is so we must try to 

 make our system in such a way as to give us a clear idea of the genea- 

 logical relations and thus try to find a practical way. 



Sponges Vary perhaps more than any other group of animals, and 

 thus we are obliged to be content in using the idea j) species « in a very 



1 E. Haeckel, Die Kalkschwämme. Bd. I— III. Berlin 1872. 



32^ 



