I THE EVOLUTION OF THE META20A 



embryos of Spongiae is not a completely isolated case ( Yol- 

 vox). On the basis of all this, Tuzet comes to the conclusion 

 that Spongiae are genuine Coelenterata, and are thus Eumeta- 

 2oa and notParazoa. In this she is followed by many zoologists, 

 even by scholars who are not French (Remane, Jagersten, Al- 

 varado). 



Considered critically, one can see that the arguments pro- 

 posed by Tuzet in favour of the old thesis which holds that 

 Spongiae are Coelenterates, have a rather weak foundation. 

 The existence of a nervous system is in no way proved for Spon- 

 giae, yet it is of great importance in this connection and Tuzet 

 tries hard to prove the contrary. The pictures of thin sections 

 that have been shown by Tuzet and her collaborators, have 

 been seen by many investigators and I, too, have able been 

 to see them. Yet no one— with one exception that will be 

 mentioned later — has classified these cells of the central strat- 

 um with plasmatic processes, as genuine ganglion-cells or 

 even nerve cells. They have always been identified as simple 

 cells of the connective tissue from the central stratum which 

 is filled up with jelly. In all probability these cells are as much, 

 or perhaps sUghtly more, irritable and able to conduct ex- 

 citement much as any other animal cell. In order to prove that 

 these cells, or at least some of them, really have a nervous 

 character it would be necessary to apply successfully special 

 selective stains, as for example methylene blue which col- 

 ours the nerve cells selectivily intra-vitam. If this has not been 

 done, then at least it would be necessary to carry out some 

 neurophysiological experiments, and achieve a positive result. 



The general behaviour of Spongiae as w^ell as the kind of 

 reactions they show to various stimuli, make it completely 

 improbable that Spongiae could possess a real net of nerves, 

 let alone sensory nerves, as these can with certainty be con- 

 sidered to exist, e.g. in Hydra, Some time ago, von Lendenfeld 

 sketched such nerve cells in pictures published by him, yet 

 nobody believed his allegations or his beautiful pictures. 

 And even, if there were some of these cells that exist— not 



