STRUCTURE AND DEVELOPMENT OF COELOI'LANA. 63 



diagram A, was supported by many other writers and the view that 

 Coeloplana represents the intermediate stage between the two classes 

 was accepted fairly widely. Nevertheless, there were several authors 

 who expressed their opinions at variance with Lang concerning the 

 origin of the Turbellaria and also on the systematic position of Coe- 

 loplana. Among such authors we can distinguish : 

 (i). One who regarded Coeloplana to be an ancestral form, from which 



both the Ctenophora and the Turbellaria have been derived 



WiLLEY ('96), (B). 



Turbellaria Turbellaria Ctenophora Turbellaria Coeloplana 



\ \ 



Coeloplana 



t 

 Ctenophora Coeloplana Ctenophora 



A B C 



(Lang) (Willey) (Korschelt & Heider, Hatschek) 



&c. 



(2). Those who considered Coeloplana as a specialized ctenophore 



Korschelt & Heider ('90), Hatschek ('91), Bourne ('00), Delage & 

 Herouard ('01), Schneider ('02) and Willey (a later work, '13), (C). 

 Many of these authors denied at the same time the existence of a 

 phyletic relationship between Coeloplana and the Turbellaria such as is 

 assumed by Lang and his followers. 



As to WiLLEv's opinion given first, I feel it unnecesary to dwell 

 upon it now, since it has been discarded afterwards by the author 

 himself, and also we have elaborate discussions of that in Abbott's ('07) 

 and Mortensen's ('12) works. 



Next, of the opinions of the writers named last, they are largely 

 in accordance with one another and differ only in minor points. I 

 shall give some instances of the opinions below : — 



Korschelt & Heider ('90), to begin with, stated : — " Man hat 

 in den merkwiirdigen Formen : Coeloplana Metschnikoivii und Ctenoplana 

 Kowalevskii directe Zwischenformen zwischen Ctenophoreri und Turbella- 

 rien zu erkennen geglaubt. Uns scheinen dieselben jedoch keine weiteren 

 Eigenthiimlichkeiten darzubieten, als sich aus dem typischen Ctenopho- 

 renbau durch Anpassung an die kriechende Lebensweise ungezwungen 

 erklaren lassen. Die Uebereinstimmung mit den Turbellarien wurde 

 sodann auf blosser Analogic beruhen. Eine solche Erklarung erschient 

 zulassig, da auch unter den echten Rippenquallen einigen Formen das 



