690 THE ANATOMY OF BOTHEIOCEPHALUS LATUS. 



Towards the sides the cells become smaller and less distinctly 

 limited, sometimes so slightly that the ground substance presents in 

 some parts the same appearance as in the Tcenice. The layer of 

 subcuticular spindle-cells is especially well-defined from the vesi- 

 cular tissue. 



The Calcareous Corpuscles (Kernkomchen, Eschr.) of Bothriocephalus, 

 as we have already noted, occur separately, and on the whole but 

 sparsely.^ They are at once most abundant and largest (up to 0"015 

 mm.) in the immature joints. They are especially met with between 

 the longitudinal fibres of the cortex, but they are not wholly absent 

 in the central layer. It appears, indeed, as if the individual speci- 

 mens exhibited great variations in the number of calcareous corpuscles 

 present. In the ripe old joints they seem not unfrequently altogether 

 absent. 



The Longitudinal Vessels and nerves, which have been already (p. 

 679) described within the head, may be traced in transverse sections 

 nearly to the sexually mature joints. They differ only in so far as 

 they increase with the growth of the body, though not in the same 

 proportion. With this increase in thickness a larger space is left 

 between them. They are not to be looked for, as in the Tcenice, 

 in the outer angles of the middle layer, but, as Eschricht ob- 

 served, further inwards, near the middle of the two lateral regions 

 (Pig. 361). 



In the ripe segments the relations are changed, since the vessels, 

 which elsewhere hardly ever measure more than 0'07 mm., and are 

 also considerably less in width than the longitudinal vessels of the 

 Tcenice, gradually become narrower till at last they are no longer 

 recognisable. They share the fate of the vessels which extend 

 beneath the subcuticula, traces of which I was able to follow on my 

 sections only as far as the neck. It cannot, however, be concluded that 

 the vessels cease here, but only that in hardened specimens they are 

 no longer to be detected, owing to their thinness, and the insufficient 

 resistance of their walls. For the elucidation of the course of the 

 vessels in Bothriocephalus, fresh specimens are necessary, and these 

 are not always procurable. This being so, it is readily intelligible 

 that the whole structure and disposition of the vascular system in 

 this worm have not yet been elucidated. We do not know whether 

 the longitudinal vessels, in tlieir course backwards, remain undivided, 



^ Landois and Sommer, and Moniez are mistaken in asserting that, in the first edition 

 of this worlt, I wholly denied the presence of calcareous corpuscles in Bothriocephalus. 

 I have always spoken only of a relative absence, and on page 425 have, in noting 

 their size, expressly stated that they agree in appearance and nature with those of the 

 larger Tainice. 



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