MORPHOLOGY OF RUDOLPHl'S SCOLEX. 373 



were no joints to be seen. Its lower end was still firmly attached by 

 a thread to the caudal bladder which collapsed." * The description 

 indeed suggests that the head was in this case destined to be set free, 

 and to wander on its own account, but from the complicated form 

 of its suckers it could hardly be regarded as a Scolex in Eudolphi's 

 sense of the term. 



Under these circumstances, then, there is little support for the sup- 

 position that the Scoleces, with which we formerly became acquainted, 

 are to be interpreted as the isolated heads of a Cysticercoid develop- 

 mental stage. It is, of course, conceivable that such a relation may be 

 afterwards proved, but we ought to bear in mind the possibility 

 that, unlike what is the case in Tcenia cucumerina, the apparent heads 

 may be regarded as Cysticercoid forms with appended, although not 

 histologically differentiated, caudal bladders. 



This is a view which essentially coincides with the idea which we 

 find, though unformulated, in Wagener's excellent treatise on the 

 development of the Cestodes. 2 What led him to it was at first only 

 the presence of a " pulsating tube " opening at the posterior end of the 

 body. This organ he regards as a characteristic peculiarity of the 

 caudal or Cestode bladder (" the head -former "), which springs from 

 the hooked embryo, and he further proves the existence of this de- 

 velopmental stage in numerous cases, and always in connection with 

 a more or less complicated and often ciliated vascular apparatus. Of 

 no less significance is the fact that Wagener frequently found the 

 Scoleces " with heads drawn back " (compare the illustrations in Tab. 

 ix. of his work), that is to say, in a position which so perfectly corre- 

 sponds with the already mentioned Cysticercus Tcenice cucumerince, that 

 one cannot refrain from collating the two forms. It is certainly strik- 

 ing and unusual in a Cysticercoid form for the Scoleces to live free 

 and mobile in the intestine of their host, but in Gyporhynchus, also 

 found in fish, we find this in an unmistakeable Cysticercoid. 



If our idea be correct, then there are Cysticercoid forms among the 

 Phyllobothria as well as among the Tcenice, whose caudal bladder is 

 both anatomically and histologically an integral portion of the head, 

 being developed inside it, and being sometimes subsequently drawn 

 back into it. 



In this retracted state the head of the Scolex is in exactly the 

 same position which we formerly found that organ occupying in 

 the Cysticercus of the dog-louse, and which we then considered as 

 mainly characteristic of the bladder-worms. The drawings which 



1 Loc. cit., p. 58. 



2 Van Beneden also directly mentions the above-mentioned Cysticercus of Phyttoboth- 

 riwn lactuca and Acanthobothrium as a Scolex (loc. cit. pp. 73, 74). 



