ON SOLLAS'S MEMBRANE IN SPONGES. 



G. C J. VOSMAER and C. A. PEKELHARING. 



With Plate II. 



I. Summary. 



»Dans tous les ordres de sciences aussi bien qu'en littérature, 

 la production d'écrits nouveaux augmente sans cesse avec une 

 effrayante rapidité." With these words of Delage *) everybody 

 will agree. But Delage was also the first to atterapt a remedy. He 

 proposes to divide a paper into two parts : — a chief one and a 

 complementary one. Although Delage's »partie principale" could have 

 been a good deal shorter, still his principle is a good one. We 

 inteud here to follow that principle. Our chief part can be condensed 

 in one line: — Sollas's membrane does not exist. This is the 

 conclusion of our investigations, The methods we used , the dis- 

 cussion and criticism of the views of other authors and the argu- 

 ments for our statement will be found as a » complementary part", 

 in the sense of Delage, to which a simple plate may give an ex- 

 planatory illustration. The cursory reader who is only interested 

 in the result of our observations thus need not spend much time. 

 On the other hand we hope that students may find sufficiënt 

 proof for our suggestion in the foUowing Unes. 



1) Yves Delage, Embryogénie des Eponges. Arch, Zool. Expér. (2) X [1892] p. 345. 



