NEW INTERPRETATION OF CNIDARIA 287 



mediate form, which was equipped with both these new pro- 

 perties, developed in all probability at the point where the two 

 lines of evolution separated. Evolution then pursued two 

 diverging directions, on one hand the line of evolution of 

 CiUata, and on the other the line of evolution of the Eumetazoa, 

 with the acoelous Turbellaria at its very beginning. 



Let us first make a closer study of the lines w-hich wxre 

 pursued by the Ciliata in their evolution. The following 

 characteristics were decisive in connection with their lines 

 of evolution: (1) the prevalence of oligomerization; it did not 

 influence the vegetative (somatic) nuclei only whose number has 

 thus been reduced to the possible minimum, i.e. to the so- 

 called macromickus which cannot be considered in spite of its 

 singleness as a homologue to the originally single nucleus; 

 oligomerization has now also been extended to the internal 

 sexual phase and as its consequence we find one sexual karyon 

 preserved. This development has led to (2) a further internali- 

 zation of the gametes themselves so that finally one andro- and 

 one gyno-gamete only are formed; copulation also becomes 

 internal. Somewhat later, oligomerization was extended to cili- 

 ation; this has led, according to the rule, to a differentiation of 

 the cilia into the ciliary organelles. This evolution had also led 

 to a new form of copulation which is externally invisible because 

 of its internalization and which is therefore better protected 

 against the external influence. 'At the same time, it had determi- 

 ned the destiny of Ciliata since they could never develop into lar- 

 ger species; they have remained microscopic Protozoa with the 

 ability to develop intensive differentiations, particularly it we 

 take into consideration the range of dimensions within which 

 they can change. A part of these properties (which was not really 

 a very small part !) had been inherited by the Eumetazoa, because 

 even before the separation of the two lines of evolution a 

 comparatively high level of organization had already been 

 reached within the frame of their small dimensions. 



It is actually not very important to know in connection 

 with our task, the evolution of Infusoria after their 



