CNIDARIA AS THE ONLY COELENTERATA 3 



that they do!— they would be a luciis a non hicendo, since they 

 would be physiologically meaningless. 



Levi (1956) made, after the publications of the school of 

 Tuzet had become known, an extensive and critical histologi- 

 cal study of Spongiae, and did not report any finding of a ner- 

 vous system or of nerve cells in Spongiae. Neither could 

 such a finding be confirmed by others, e.g. G. Eberl (Eberl, 

 1950), an excellent histologist from Vienna who used num- 

 erous staining techniques in her work. Yet in spite of all 

 this the propositions as well as pictures published by Tuzet 

 have found acceptance in many schoolbooks, especially in 

 France. 



Neither did Miss Tuzet succeed with her — it can be truly 

 said — attempt to disprove the law of the supposedly inversed 

 sequence of body layers in Spongiae. As is well know^n, Metsch- 

 nikoff and many other famous zoologists after him, among them 

 particularly Yves Delage, have shown that in the ontogenies 

 of Spongiae, the early morphogeny proceeds along very parti- 

 cular lines. We get the impression that during the morphogeny 

 of Spongiae a process takes place that is opposite to the process 

 w^hich can be observed in Eumetazoa. The primitive "ecto- 

 derm," i.e. the foremost part of the spongula, develops into 

 the definite "entoderm," and the primitive "entoderm" into 

 skin, this into the "ectoderm." For this reason Spongiae have 

 been called Enantiozoa (i.e. animals with the two strata of 

 body inversed) by Delage. Naturally, this inversed character is 

 relative only i.e. in comparison to the development that can 

 be observed in Eumetazoa. In fact, wx have here a particular 

 characteristic of Spongiae w^hich has been developed during 

 the course of their own phylogeny. It is therefore better not to 

 speak in connection with Spongiae about an ecto- or an ento- 

 derm but rather to use special names, e.g. pinacoderm and cho- 

 anoderm. The facts themselves cannot be changed. Yet Tuzet 

 gives a description of an isolated case among Calcispongiae 

 where the extroversion of the spongula blastoderms can be ob- 

 served. A comparison wdth the only slightly similar case in the 



