278 THE EVOLUTION OF THE METAZOA 



movement which is connected with it; (4) the fact that the 

 interior of their bodies consists of three body layers, with 



(a) a more or less solidified external layer, with fine variations 

 especially as regards its fibrillar and sculptural nature, 



(b) a somewhat softer middle layer (without streamings) which 

 contains nuclei, the contractile myonemes, and the contractile 

 emunctories (vacuoles), (c) the streaming digestive internal 

 layer (cyclosis), with the digestive vacuoles; (5) a cytostome; 

 (6) a cytopharynx, and not unfrequently (7) a cytopyge; (8) the 

 trichocysts; (9) a hermaphroditic regime combined with pair- 

 ing and with an internal fertilization; (10) the asexual repro- 

 duction by means of transverse division. 



All these, and other similarities which are not mentioned 

 here, should thus be accidental analogies or parallelisms! Can 

 this be probable? The improbability of such a group of analo- 

 gies becomes even less acceptable if we succeed in clarifying 

 or in rationally solving the most important differences that now 

 seem to exist between these two animal groups. 



There is one more important reason why we should consider 

 these similarities as true homologies and why we should 

 accept the derivation of the Acoela, as the lowest Eumetazoa, 

 from some infusorial ancestors as more probable than the 

 derivation of Coelenterata from some colonies of Flaeellata. 

 This reason can be found in the continuity of development of 

 the whole polycellular unit which I will return to discuss on a 

 later page. It is quite natural that the similarities that exist 

 between a holotrichous infusorian, as it is now known and a 

 recent acoelan, are explained by those who adhere to the widely 

 accepted colonial theory, as if they were analogies or paral- 

 lelisms only; they are logically obliged to come to this conc- 

 lusion. It is easy to understand why these scholars try to bring 

 forward possibly good arguments against the "plasmodium 

 theory" ("Plasmodiumtheorie") as it was called by Steinbock. 

 Thus Remane wished that those scholars who accepted the 

 Plasmodium theory could bring forward evidence in the 

 form of "transitional forms," "proved patterns," "certain in- 



