22 ARTHUR DENDY. 



ausgefallt sei ;" and the only conclusion at which he is able 

 to arrive with regard to the question of Sollas's membrane 

 is that it does not exist, and that Professor Sollas and I 

 have only misinterpreted what it has been reserved for him 

 to correctly describe. But in spite even of a preconceived 

 " theoretische Unwahrscheinlichkeit " I adhere to my original 

 opinion. For my own part, I am unable to see where the 

 theoretical improbability comes in. Quite recently Mr. Carter 

 has, in a private letter, afforded me valuable corroborative 

 evidence of the existence of Sollas's membrane. He says, 

 " I have seen in the brim of the collar of the Calcisponge 

 spongozoon plastic amalgamation like that produced by two 

 semi-fluid bits of gum — under which circumstances, if all 

 became amalgamated, then you would have Sollas's membrane. 

 Might it not so happen that at one time they may be so 

 amalgamated and at another not, and thus produce the dif- 

 ference ? " That Sollas's membrane originated in the almost 

 accidental manner here indicated there can be no doubt, but I 

 am inclined to think that in many sponges it has become a 

 more or less fixed and constant character — a view supported 

 by the fact that, as I shall show later on, it is still recognisable 

 when both collars and flagella are withdrawn. It is exceed- 

 ingly likely from the nature of the case that it may have 

 originated independently in several groups, so that in each 

 group forms with and forms without it may exist. If so it is 

 only another instance of that homoplasy so characteristic of 

 the Porifera. 



I am not aware that there is anything particularly new in 

 Dr. von Lendenfeld's observation that " die Kragenzellen 

 stehen nicht frei auf der Oberfliiche der Zwischenschicht, 

 sondern sie sind in dieselbe Eingesenkt " (16). Indeed, in 

 my paper on Stelospongos (2) I have said, "1 have not 

 been able to trace any definite outline to the body of the cell 

 which is embedded in the highly granular ground-substance." 

 It is amusing to see Dr. von Lcudenfeld so vigorously opposing 

 one of my observations which does not happen to fit in with 

 his idea of the fitness of things, and at the same time taking 



