PREVIOUS INTERPRETATIONS OF CNIDARIA 215 



and in Euciliata as a transverse division. It is not difficult to 

 imagine that budding had evolved out of division during the 

 sessile way of life; this can be observed as early as in Ciliata 

 (Euciliata on one hand, Suctoria on the other). 



We can rightly reverse the situation and can maintain that 

 the facts observed in connection with asexual reproduction 

 give support to our interpretation of the origin of Cnidaria 

 from Turbellaria. In the freely-moving Turbellaria transverse 

 division only appears; they inherited it from their euciliate 

 ancestors both in its primitive form as an architomy as well 

 as in its more progressive form as a paratomy. It is true that 

 this transverse division does not appear equally well deve- 

 loped in all animals that belong to the class Turbellaria because 

 it is coordinated with the way of life and the degree of plas- 

 ticity; we can find it mainly in their "lower" subgroups: in 

 Acoela (cf. the recent studies by P. Ax and Schulze and O. 

 Steinbock) and Rhadocoela, in Tricladida, and in the terrest- 

 rial Planaria. These are animals w^hich reproduce regularly only 

 by means of division. In the terrestrial Planaria, fragmentation 

 can frequently be observed which slightly resembles laceration 

 such as occurs in Actiniae. It can be easily understood that in 

 Turbellaria no budding has been developed because of their 

 active movements. Yet in spite of this we find in some Rhab- 

 docoela that paratomy has reached a state which is so similar 

 to budding that experts in Turbellaria have believed that it 

 really was budding. 



Transverse division appears, as can be expected from our 

 standpoint, in the primarily solitary Anthozoa, even if it is 

 not frequent. The best known case is that of Gonactinia proli- 

 fera; Carlgren was able to show that here transverse division 

 occurs serially in the form of a paratomy. The case of Fmgia 

 which has also been closely studied shows that transverse di- 

 vision can be found among Madreporaria, even if in a some- 

 what different connection (unequal division and the alterna- 

 tion of generations). This type of division was taken over by the 

 Scyphozoa from their anthozoan ancestors; here it is called 

 15* 



