346 THE DEVELOPMENT OF CESTODES. 



The substance of the newly formed head consists of the same 

 small nucleated cells which we found in the subcuticular sheath, 

 whence, indeed, it originated. As soon as it begins to raise itself 

 more prominently, and to grow out like a clapper, one can see on the 

 surface turned towards the bladder-cavity a thick envelope of a fibrous 

 character. The head of the bladder-worm is, in other words, enclosed 

 in a sac which separates it from the rest of the body, and which can 

 still be recognised as a special formation when the enclosed cells have 

 completed their metamorphosis. I have proposed for this envelope 

 the name "receptacle" 1 (receptaculum scolecis), and am still inclined 

 to support this proposal, although I have meanwhile come to hold a 



FIG. 188. Various stages in the formation of the head of Cysticercus cJluLotce t 

 showing the receptacle. ( x 45.) 



different opinion as to the nature of the organ in question. I was 

 formerly of opinion that this receptacle originated from a differen- 

 tiation of the cellular mass of the head, and was indeed genetically a 

 part of the head, but I have subsequently become convinced that it 

 belongs to the inner layer of muscular fibres which run inside the 

 bladder, and which are pushed into a sac by the elevation of the head, 

 the cells of which have a more peripheral position. Of course, one 

 must not suppose from this statement that the receptacle is simply 

 formed by a distent ion of the inner layer of muscles, and that it only 

 contains the muscular fibres which formerly overlaid the cellular rudi- 

 ment of the head. On the contrary, there can be no doubt that new 

 elements become associated with these old muscular fibres during the 



1 Von Siebold has also used this term in his work on tape-worms and bladder-worms, 

 but in quite another sense, namely to denote the proper body of the bladder- worm (the 

 enlarged six-hooked embryo). Kuchenmeister also speaks of a receptacle in the new 

 edition of his work on Parasites (p. 61), but understands by the term the primitive rudi- 

 ment of the head, which he does not recognise as such, but regards as a brood capsule, 

 which subsequently bears the tape-worm head. Indeed the description he gives of the 

 development of the bladder-worm is such a strange mixture of capricious imagination and 

 confused representation, that I must decline entering into its details. 



