430 University of California Publications in Zoology. [VOL. 6 



Tiere, die ohne ein wahres Vorderende, d. h. einen Kopf zu besit- 

 zen, mit dem aussersten Hinterende sich an der Darmwand fix- 

 ieren und mit ihren relativ vordersten Korperende frei in den 

 Darm hineinhangen. " He then proceeds to show that, first, the 

 presence of a differentiated intermediate portion between the 

 anterior and posterior segments of the body, secondly, the detach- 

 ment of the posterior segment and its transformation into the 

 sexually mature animal, and lastly, the location of the growing- 

 zone in the penultimate region of the body, are conditions whose 

 analogues can be readily found in other worms and also in 

 echinoderms, bryozoans, etc. On the last and probably most im- 

 portant point, the location of the growth-zone, he sums up the 

 evidence very briefly as follows : 



"Ob wir also die normalen Wachstumserscheinungen, ob wir Kegenera- 

 tion oder die der autotomischen Teilung vorausgehenden Processe der Seg- 

 mentvermehrung betrachten: uberall finden wir dass sich die Wachstumzone 

 beiden genannten Tieren an aussersten Hinterende des Korpers befindet. 

 Bei der von mir vorgeschlagenen Orientierungen der Cestoden schaffen wir 

 also in bezug auf die Wachstumsverhaltnisse keinen Ausnahmefall sondern 

 erhalten im Gegenteil erst so die Moglichkeit, das Wachstum der Cestoden 

 durch Proliferation am Collum mit demjenigen anderer Vermes konform 

 auf zuf assen. ' ' 



These considerations, arising from facts of comparative 

 embryology and morphology of the invertebrates, taken together 

 with those arising from a study of the morphology of the primi- 

 tive genus Gyrocotyle, afford a warrant for serious question of 

 the validity of the generally accepted orientation of cestodes. 

 Furthermore, they constitute a more or less successful effort to 

 take this question out of the realm of "self-evident" hypotheses 

 incapable of either proof or disproof where, as Cohn pointed 

 out, it has too long existed. Further embryological research, 

 especially on such forms as Ampliiliiia and Gyrocotyle, is greatly 

 to be desired ; from this field the final word on the question must 

 be obtained. All the facts now at hand, however, seem to show 

 that this decision will be in direct opposition to the generally 

 accepted belief, and will place the organ of attachment in ces- 

 todes at the posterior extremity of the strobila. 



