NEW INTERPRETATION OF CNIDARIA 347 



this point. They all waver between the two extreme inter- 

 pretations because they do not know of any exact method 

 by which to determine the absolute age of individual animal 

 types (frequently we cannot even determine their relative age), 

 nor have they available any evidence in the form of fossils. 

 One of these interpretations believes that there is no difference 

 between the process of specialization, or the evolution of 

 species by way of slight steps in the direction to such a dif- 

 ferentiation, and the evolution of very large types of animals. 

 According to this interpretation the "geologic age" can be 

 considered as the only factor; the whole evolution had been 

 uniform and gradual, yet it was not shared by all the species 

 or all the lines of evolution. 



The opposite standpoint has been defended above all by 

 the palaeozoologists, and it is connected with the names of 

 several zoologists; it believes in special, i.e. revolutionary, 

 changes which had led to the formation of completely new 

 animal types. We cannot find as many animal types as would 

 be expected if evolution had constantly been strictly slowly 

 evolutive, and never revolutionary, marked by sudden greater 

 changes. The origin of the minor taxons is now already well 

 enough known. Important sudden changes could also be 

 observed in various cultures and experiments. It is therefore 

 almost certain that the new types do not emerge in the w^ay 

 as w^as formerly thought, so that a young bird could 

 suddenly emerge from an egg of a reptile. It is also clear that 

 in the development and the preservation of a certain type 

 of structure much can also depend on the external factors 

 (the conditions of the environment). It is not my task to 

 discuss here in detail the problem of macro-evolution versus 

 micro-evolution. Still I wish to emphasize that I accept 

 the standpoint as represented by neo -Darwinism combined 

 with that of the genetics. As in the case of numerous other 

 problems of biology we consider the phenomenon of the 

 origin of new animal types to be a complex factor. It can be 

 only approximately conjectured where the limit is between 



