12 THE EVOLUTION OF THE METAZOA 



taken place in several other organs (intestinal diverticulum, 

 swimming plates). 



In both groups we find their tentacles equipped \\ ith parti- 

 cular specialized monocellular gland cells; on one hand with 

 colloblasts, and on the other with cnidae. The tw^o forms are 

 so widely different from each other that they cannot be con- 

 sidered to have developed one from the other. It seems, how- 

 ever, as if Enchlora rubra, a ctenophore, stood in apparent 

 contradiction to these observations. This ctenophore can 

 rarely be observed and it does not have colloblasts in its two 

 tentacles, but instead genuine cnidae; these are not only "drawn 

 up" (i.e. ready to be used) but also kept in reserve, as is the 

 case with medusae which are genuine Cnidaria. A detailed 

 analysis of this case (Hadzi, 1951, 1959, 1959a), however, has 

 show^n that wx do not have here a real exception, but that 

 instead this phenomenon is not limited to Euchlora only. In 

 all probability this is a case of the so-called kleptocnidae, i. e. 

 cnidae that have remained alive and that have been stolen by 

 the predator from prey which had been devoured. Taku Komai 

 (1935, 1951), a well-known Japanese zoologist, who has recently 

 had the good luck to be able to make a detailed study of 

 Euchlora and who in his work first expressed his opinion that 

 these cnidae actually belong to the animal, has later become 

 convinced that we really have here a case of kleptocnidae. 

 Eiichlora subsists mainly on Narcomedusae and it seems that it 

 has become so specialized that it has ceased to produce collob- 

 lasts, its original weapons, and instead "works" exclusively 

 with cnidae taken over from its usual prey. This certainly is a 

 very interesting case and it is at the same time at least one 

 more fact which supports our thesis that the Ctenophora 

 cannot be directly related to Cnidaria. 



Besides the differences which have been already mentioned, 

 between the tentacles of Ctenophora and medusae, there is 

 one more which makes it completely impossible— in spite of 

 their great external similarities— to consider the two organs as 

 homologous or descending from the same origin, or even to 



