THE NEW GENEALOGICAL TREE 405 



organs, and by way of an intensive growth in length combined 

 with a sinuous type of movement, under the presupposition 

 that the perigastrocoele had consisted from the very begin- 

 ning of several segments. 1 wish to emphasize that for 

 ecological and physiological reasons it is improbable that the 

 polychaetous Annelida evolved from such animals as the semi- 

 sessile or completely sessile Tentaculata. The facts such as 

 the existence of transitional forms between the Annelida and 

 Phoronoidea, suggest that there had been an opposite line 

 of evolution. 



Besides the interpretation which has been proposed in the 

 present study, and the interpretation which we have rejected, 

 there is one more theory which tries to explain the origin 

 of the polymerous state. We can mention it only briefly. There 

 have been besides older zoologists such as Haeckel, some 

 modern scholars (e.g. Steinbock) who have believed that 

 the so-called zooidal hypothesis could be the most acceptable 

 interpretation. According to this theory a kind of a chain- 

 Hke complex develops from an oozooid, or a primary person, 

 by way of an incomplete transverse division which can easily 

 pass over into a budding. This complex had afterwards been 

 changed by way of a subsequent complete integration into 

 a uniform polymerous state. It must be admitted that many 

 facts can be referred to by the adherents of the zooidal hypo- 

 thesis. Thus above all the not so rare phenomenon of an 

 initially incomplete repeated division which can be observed 

 among the Turbellaria (the chain -like formation of the mi- 

 crostomous species). This is certainly a case of an only sUghtly 

 modified asexual reproduction which could never possibly 

 have led to any permanent polysegmented state. The case of 

 the Cestoda which is also frequently mentioned in this con- 

 nection belongs, I think, to the completely different category 

 of morphogenesis than the development of a polymerous 

 state. 



The evolution of the Cestoda stands entirely under the 

 influence of their endoparasitic way of life which has a very 

 27 



