696 THE ANATOMY OF BOTHRIOCEPHALUS LATUS. 



only in so far as it is internally clad by a somewhat firm, doubly 

 contoured cuticle, which is continued at the outer openings directly 

 into the cuticle of the cloaca, and like it rests on a distinct subcuti- 

 cular layer of cells. This can hardly, of course, be compared with the 

 subcuticular layer covering the body. It has but an insignificant 

 thickness, and gradually vanishes posteriorly towards the seminal 

 vesicle. Like the latter, this zigzag coiled posterior portion of the 

 canal is usually filled with semen, and much widened, while the 

 extended terminal portion remains always empty and closed. 



The cirrhus-pouch, which surrounds the above-described canal like 

 a bulb, protrudes the anterior portion of the cirrhus, and thus brings 

 about copulation. The muscles admit of simpler and sharper analysis 

 than in Tcenice, and are evidently disposed for the discharge of this 

 function. 



The external wall (Eschricht's "capsule") is formed of a thick 

 sheath of muscles, whose fibres, as Landois and Sommer rightly 

 observed, generally run in the longitudinal direction of the bulb, 

 extending from the rounded dorsal pole to the genital pore. Near 

 the latter they bend for the most part from their former direction, 

 mingling with the adjacent longitudinal fibrous bands, and ramifying 

 in the cortical layer. By the contraction of these fibres the cirrhus- 

 pouch is pressed diagonally downwards against the yielding floor of 

 the cloaca, so that the latter is arched outwards, and the inferior seg- 

 ment of -the bulb protruded like a plug. The canal is not, however, 

 evaginated without the pressure of the circular fibres, which lie partly 

 isolated among the longitudinal and partly united in plexiform fashion, 

 penetrating (iri the anterior half of the cirrhus-pouch as far as the 

 evagination occurs) even into the deeper connective-tissue masses, and 

 being thus eminently capable of affecting these. Under the pressure 

 of the circular fibres the inferior pole of the pouch assumes first of all 

 a mammiform shape, until, through the evagination of the enclosed 

 canal, whose lips represent the pars minoris resistentice, the cirrhus 

 proper is subsequently protruded. It need not be specially men- 

 tioned how during this operation the coils of the canal are unwound 

 and the spiral turns of the posterior portion straightened. 



Not only the protrusion of the cirrhus, however, but also its retrac- 

 tion, is fitly secured by radial fibres, which spring on every side from 

 the muscular envelope of the cirrhus-pouch, penetrating the cortical 

 substance at varying intervals, finally uniting with the external wall 

 of the pouch, that is, with its subcuticular layer. The cirrhus-pouch 

 has its own special retractor muscles, in the form of sagittal fibres, 

 which pass from the dorsal surface of the joint, and are inserted on 

 the adjacent segment of the muscular capsule. 



