728 OCCURRENCE AND DEVELOPMENT OF BOTHRIOCEPHALUS LATUS. 



Fig. 391. — Transverse section through 

 the body of a larva of Bothriocephalus. 



Piestocystis, is explained by the absence of the muscular suckers, which 

 are so specifically characteristic of the head of Tmnia. And the fact 

 that in place of the four transversely placed suctorial grooves only 

 two occur in Bothriocephalus, is also explicable ; for it can be easily 

 proved by means of sections that the invaginated head of the bladder- 

 worm from the pike at first appears 

 only as a flattened cavity, which is 

 lined by a continuation of the cuticle, 

 and which, extending in the direction 

 of the shortest diameter (i.e. at right 

 angles to the broad surface), sinks in 

 for some distance from the anterior 

 end of the" body. Only after more 

 minute observation does one perceive 

 around the cavity (especially in 

 transverse section) the parenchyma of the invaginated head with its 

 muscular fibres, which form externally a sort of receptaculum, dis- 

 tinctly separating the head from the rest of the body. On the right 

 and left, close to the receptaculum, one can now 

 distinguish the lateral nerve cords. 



How this larva changes into the jointed tape- 

 worm after its transference to the final host has not 

 yet been investigated. Braun's observations, which 

 alone are available on this point, only show that, 

 soon after entering the digestive apparatus of the 

 final host, the larva stretches out the hitherto 

 retracted head, and fastens itself by its aid to the 

 intestinal wall ; and that, after losing the calcareous 

 corpuscles, which were previously very numerous, 

 it grows with considerable rapidity, so that in a few 

 days it may measure 6 cm. in size, and exhibit a 

 somewhat indistinct segmentation. The increase in 

 size affects not only the body, but also, and perhaps 

 -.F^'^' , ^^'^:~,?\ sooner, the head, whose form at the same time is 



gittal longitudinal no-, it, 



section through the ^o^Q definite, and like that of the adult worm. 

 bladcTer^worm'^from Whether the larval body is entirely or partially 

 the pike. ( x 40.) lost during tliis modification is uncertain. The de- 

 t^o'''onrside''of ae scription given by Braun almost leads us to infer the 

 middle line, so that Contrary, although in his observations no special 

 toriafp'itf limit The ^tt^ntion secms to have been directed to the history 

 latter externally. of the larval body. The histological structure in no 

 way contradicts such a supposition, for, as we have 



already seen (Fig. 391),.^.the iaryal body in all essential points 

 Digitized by Microson® ^ 



