PREVIOUS INTERPRETATIONS OF CNIDARIA 199 



cnidae and which can be used by the animal when it catches 

 its living prey? Colloblasts had ultimately been developed from 

 the same source as cnidocytes, i.e. from the cells of the skin 

 glands of the oldTurbellaria; in both these cases, however, 

 the development took place independently, and therefore 

 parallel, and this is the reason why it is senseless to combine 

 Ctenophora, as Acnidaria, with Cnidaria into one higher taxo- 

 nomic unit of Coelenterata. The main difference that can be 

 noticed between colloblasts and cnidae is that colloblasts do 

 not represent a firm and formed unit (glutinous kernels 

 cannot be attributed to it !) and that they function as a glutinous 

 substance without the aid of an explosion. In spite of the fact 

 that they form two types of elastic, or contractile, filaments 

 (a straight and a spiral filament), they have reached a lower 

 level of differentiation than the one that has been reached by 

 cnidae. 



Thus we return now to the cnidoblast as the skin gland cell 

 which shows the best developed differentiation and speciali- 

 zation in the entire animal world. Once separated from its 

 "maternal cell" (cnidocyte, stinging cell, nettle cell), or after 

 the death of the maternal cell, the capsule or the nematocyst, 

 though itself not alive, even if it possesses a complex structure, 

 can continue to function in a foreign environment as is proved 

 by the so-called kleptocnidae. The fact has frequently been 

 forgotten or quietly passed over (e.g. in the book by Hyman) 

 that cnidocytes are originally monocellular gland cells and 

 that they did not appear as such, i.e. as fully developed, 

 suddenly in the Cnidaria; they had a long phylogenetic develop- 

 ment behind them which leads by way of Turbellaria down to 

 the Protozoa. It has already been mentioned that similar forms 

 had probably been developed polyphyletically as early as in 

 Protozoa. Even a cursory comparison of the "nettle capsule" 

 of the dinoflagellate Poljkrikos schwart^i, w4th the trichocyst 

 from the paramecium and from the so-called polar capsule of 

 the Myxoholm (Cnidosporidia), with cnidae of Cnidaria, and 

 finally with various partly solid secretions of the turbellarian 

 14* 



