294 THE ANATOMY OF CESTODES. 



series of spindle cells with the longitudinal musculature of the neigh- 

 bouring joint. It is, however, only the deeper layer of the longitudinal 

 muscles which exhibits this relation. The more superficial fibres 

 have indeed their spindle cells, but these bend at an early stage out 

 of their longitudinal direction and attach themselves to the cuticle. 

 They resemble the ordinary subcuticular cells, except in this, that 

 they do not lie at right angles to the cuticle, but at an acute angle 

 corresponding to the direction of the connected fibres. This cannot, of 

 course, be considered an essential difference, since even the sub- 

 cuticular spindle-cells bend from their normal direction at the in- 

 curved terminal borders of the proglottides, and apply themselves to 

 the cross muscular fibres, here bent into the form of a bow (Fig. 149). 

 These arrangements are best studied on sagittal longitudinal 

 sections, which show us further that (Fig. 149) the middle layer of 

 the individual proglottides, although passing through the isthmuses 

 without interruption, and thus, like the cortical layer, running the 

 whole length of the worm without breach of continuity, 

 differs widely at various situations in the structure of 

 its sagittal muscles. Not only do these become con- 

 siderably stronger at the ends, but they curve into 

 little arches, as has been already noted (p. 291). In 

 this way the generative organs are, to some extent, 

 bounded and restricted in the individual joints. 



There is no need to point out how much the libera- 

 tion of the proglottides is facilitated by the above 

 arrangements. It is also evident that the liberation 

 will be effected by muscular contraction. I believe 

 that the sagittal muscles are by their structure specially 

 efficacious in the process of liberation, for they are able 

 by contraction to flatten themselves, and thus con- 

 laat joints oiTcmia siderably to expand the middle layer. It is, indeed, 

 saginata about to the middle layer which first ruptures, while the peri- 

 size. ' ' pheral parts, and especially the lateral borders, often 

 retain their connection for a while (Fig. 150). 

 In the interior of the head the arrangement of the muscles has 

 been specially modified on account of the presence of suckers and 

 hooks. The various muscle-groups of the body can be followed a 

 considerable distance through the "neck," but their arrangement varies 

 very much according to the nature of the attaching apparatus. "We 

 will now simply refer to the detailed description which we shall 

 afterwards give of the head both in Tmnia and in Bothrioceplialus, 

 and will only note that these two types do not by any means exhaust 

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