356 THE DEVELOPMENT OF CESTODES. 



In the great majority of species the productive power of the 

 bladder is exhausted in the formation of a single tape-worm head, as 

 in the bladder-worms proper, which were referred to the genus Cysti- 

 cercus by the older Helminthologists. The cause of a multiplication of 

 heads is unknown ; therefore, we can hardly say that it is not possible 

 for a Cysticercus to have at a time two or three heads, instead of only one, 

 and isolated instances of polycephalous bladder- worms have indeed been 

 chronicled, 1 though my observations on Cysticercus longicollis of the 

 shrew (Hypudceus), (the young stage of Tcenia crassiceps of the fox), to 

 which most of these reports refer, have caused me to regard these 

 alleged instances with some suspicion. 2 The lappet-like appendages 

 of the caudal bladder, which have been regarded as new heads, turned 

 out to be simple diverticula of the bladder, that is to say, they owed 

 their origin to an irregular growth, determined perhaps by pressure 

 or traction. It seems to be very likely that these structures have a 

 mechanical cause, 3 since I once saw in Cysticercus pisiformis a similar 

 diverticulum firmly connected with the enveloping connective tissue 

 capsule, and since the bladder-worms of the common Tcenia of man 

 often grow out into irregular tubes in the subarachnoidal spaces of 

 the brain, which, with their adherent bladders, sometimes have a quite 

 racemose character, but yet never form new heads. 



This polycephalous condition, at most an exception in the Cysticerci, 

 occurs constantly in the "stagger-worm" of the sheep; that is, in the 

 cystic stage of the Tcenia ccenurus of the dog. In this bladder-worm, 

 which is found in the cavities of the skull, a group of three or four 

 heads is present from the first, and the number is continually increased 

 up to several hundreds. The new heads are 

 budded out beside and between the older, and are 

 not irregularly scattered over the whole surface of 

 the bladder, but occur in groups, and only in one 

 (anterior ?) segment of the vesicular body. 



The Ccenurus (Tcenia multiplex of Goze) is 

 related to the Cysticercus as a compound to a 

 simple animal a sufficient reason for systematic 

 FIG. 203. Heads of zoologists to separate them. But apart from the 

 multiplication of these heads, the structure is the 

 same. Each of these many heads arises just as the single one did 

 (Fig. 197) ; in origin and structure they are quite analogous. Nor 

 can we regard it as a special characteristic of the Ccenurus that the 



1 Especially by Bendz in Olcen's I sis, p. 814, 1844. 



2 V. Siebold comes to a similar decision, Zcitschr. f. wiss. Zool., Bd. ii., p. 226, 1880. 



3 The "double monster" of Cysticercus longicottis, figured by Bremser in his " Icones 

 Helminthum" (Tab. xvii., Fig. 14), is probably to be regarded as due to the above cause. 



