YOUNG STAGES OF THE DIBOTHRIA. 377 



end, like a head, bears the two suctorial pits, while the rest of the 

 body develops the sexual organs. What is in the other Cestodes 

 spread over two successive generations, seems in Archigeles, as well as 

 in some other forms, to be condensed into a single developmental 

 stage ; for the animal is not a colony with head and sexual animal, 

 but a simple head-bearing and sexually mature flat- worm. 



According to all appearance, this is, however, not the only Cestode 

 which develops in the manner described. Wagener x tells us that in 

 TricenophoTUs, so long as it remains encapsuled in the liver of the 

 fish that is to say, lives in its intermediate host there is seen 

 attached to the thick fore-part of the body, which bears the attaching 

 apparatus (pits and hooks), a ribbon-like caudal appendage, almost 

 half as long as the entire body. Bounded in front by a constriction, 

 and very different in structure from the rest of the body, it is dragged 

 about by the motions of the animal like a lifeless mass. It is thus 

 undoubtedly a peculiar structure, and comparable to the caudal 

 bladder of the other Cestodes, in so far as it is at first destitute of the 

 fore-part of the body, and itself represents the worm. 



In the other Dibothria, so far as we know, a special caudal ap- 

 pendage is never present. The embryo apparently grows by simple 

 elongation into a cylindrical or tape-like 

 worm, which then forms the attaching 

 apparatus at its anterior end, in a way A 

 which has not yet been ascertained. These jj 

 developmental processes have a general 

 resemblance to those which we formerly 

 saw to be characteristic of Eudolphi's 

 Scoleces (and other Cysticercoids), only that FIG. 221. Larva of a Bothrw- 

 in this case the share which the embryo ce P h(du8 from the smelt - 

 takes in the formation of the adult animal is much more than merely 

 structural. 



In many cases the Dibothrian tape-worm attains, even in this 

 intermediate stage, a considerable size. Thus Diesing 2 describes, 

 under the name of Spargarum reptans, what was probably nothing 

 else than a larval form of Bothriocephalus, which was a foot long, and 

 occurred in no fewer than thirteen mammals, twenty-four birds, and 

 fifteen amphibians, all in Brazil. It was sometimes encysted under 

 the skin, or between the muscles, and sometimes occurred free in the 



1 Loc. cit., p. 26 et seq. Zeder, however, made the same observation before Wagener 

 ( "Nachtrag zu Goze's Naturgesch. , " p. 414). He was even led by it to rank this worm 

 (as Vesicaria lucii) with the Cysticcrti. 



2 DenJcschriften der Wiener ATcad., Bd. ix., tab. ii., p. 174, 1855. 



