678 



DESCRIPTION OF THE BOTHRIOCEPHALID^. 



spending to the form of the head. They are not, however, stretched, 

 as in the jointed body, but are disposed in curves corresponding to 

 the concavity of the suckers. Towards the sides the fibres separate 

 in a fan-like manner, until they severally reach the external surface 

 of the head, and are there inserted. Their function is probably to 

 bring together the lateral portions of the head, which extend as sort 

 of lips beside the suctorial grooves, and thus to narrow the grooves 

 and assist fixation. 



The effect of these muscles is increased by fibres, which are dis- 

 posed at right angles to the internal cavity of the grooves, and which 

 probably play the same rdle as the radial muscles in the suckers of 

 Taeniadae. In the median layer of the head, between the two grooves, 

 these fibres are stretched, as ordinary sagittal muscles, between the 

 dorsal and ventral surfaces, while they extend transversely in more or 

 less diagonal course, through the lip-like projecting lateral borders. 



The longitudinal fibres exhibit a disposition which, like that of the 

 transverse strands, is conditioned by the form of the head. They are 

 not limited to the middle portion alone, but 

 traverse, in considerable numbers and in 

 closely packed groups, the lateral portions, 

 which project dorsally and ventrally, so that 

 they form in cross section an almost H -shaped 

 figure. Their contraction causes a shortening 

 of the head, and especially of the lips, in con- 

 sequence of which the latter are slackened 

 and lose their grip. The longitudinal fibres 

 are therefore to be regarded as the antagonists 

 of the other head muscles described above. 

 They are aided to some extent by fibres which 

 pertain to the convex external surface of the 

 head, and pass from one region to another 

 like tendons, with spans of varied length. 

 Although but weakly developed and few in 

 number, they are probably sufficient to approximate the margins of 

 the external surface, and thus to separate the lips of the suckers and 

 widen the grooves. 



The Cutaneous Glands. In well-stained heads of Bothriocephalus 

 latus (and it is only in such that the fibrous strands here described 

 can be clearly followed) one can detect between 'the spindle-shaped 

 cells of the subcuticular layer, both in the suctorial grooves and else- 

 where, a number of intensely stained bodies of bottle-like shape (0'017 

 mm. long by O'OOS-0'01 mm. broad), which have their necks turned 

 outwards, and which sometimes allow their contents to pass out in the 



FIG. 355. Transverse sec- 

 tion through the head of a 

 young Bothriocephalus latus. 

 (x 55.) 



