NEW INTERPRETATION OF CNIDARIA 291 



This, however, does not mean that it does not actually occur 

 since we are still far from knowing much about the biology 

 of the Acoela. No extensive and planned experiments in their 

 culture have been made so far. Many more precise investi- 

 gations have been made in connection with the Infusoria. In 

 these w^e can find a clearly developed progressive evolution 

 towards a sexualization which has led to an explicit sexual 

 dimorphism. During the early stage of this development the 

 individuals do not show any morphological difference what- 

 ever, in spite of the fact that they are already physiologically 

 differentiated. Here we can find an analogy to hologamous 

 isogamy. The behaviour of individuals with different bio- 

 chemical polarizations is similar to the behaviour of males 

 and females of the gonochoristic or dioecious Eumetazoa. 

 The individuals with the opposite "signs" are mutually at- 

 tracted, and this leads to a union, to a pairing. In the actual 

 sexual generation, in the gametes, the differentiation can take 

 place in two directions only (bipolar: + and — ), if we 

 disregard the indifferent middle, the 0-point (e.g. the worker 

 bees, and other similar cases), so that two sexes only can be 

 developed. In the generation of gamonts of Euciliata, however, 

 development has led, as it is well known, to the formation 

 of several "mating types." In the species of Infusoria we could 

 correspondingly expect several morphologically different forms 

 which would answer the several "mating types." It is not 

 known to me whether anything of this kind has been observed 

 till now. Yet we find in the Infusoria, above all in their sessile 

 species, sexual dimorphism further developed, in spite of their 

 hermaphroditic state. On a lower level the difference is mainly 

 of a quantitative nature, as is shown by the frequently quoted 

 example of the Opisthotruhium janus. We speak in this connec- 

 tion of macro- and of micro -con jugants which are developed 

 by means of a division that takes place before the conjuga- 

 tion. This division, however, should not be called— as it 

 usually is— a progamous division; the true progamous divi- 

 sion takes place during the conjugation in the gametic karyons 



