402 WILLIAM A. nASWKLL. 



wliich it lias undergone a reduction in thickness. A similar 

 reduction is observable in the internal longitudinal layer of 

 muscular fibres (('. /. m.), wliicli are well developed in all parts 

 of the strobila^ and very conspicuous in transverse sections 

 owing to their highly refracting character, whereas in the 

 free proglottides they are barely discernible in transverse 

 sections, and in longitudinal appear as a few inconspicuous, 

 often degenerate, fibres. 



The nervous system (fig. 3, fig. 4, n. c.) is in no way 

 remarkable, consisting of the usual head-ganglion in the 

 scolex, and the pair of longitudinal nerve-cords with their 

 branches and commissures. In the separate proglottides, 

 owing to the reduction in the thickness of the subcuticular 

 cellular and internal longitudinal muscular layers, the nerve- 

 cords come to be situated more superficially than in the 

 strobila. They meet anteriorly in the " head,^' where there is 

 a slight thickening of the nature of a rudimentary ganglion. 



As in many other forms, two of the four longitudinal 

 excretory vessels of the anterior region — the dorsal pair — 

 become reduced greatly in diameter in the posterior pro- 

 glottides. In the last proglottis these open on the exterior 

 at the posterior end. In the free proglottides (fig. 3) only 

 the ventral pair remain. These are very narrow towards the 

 anterior end, while posteriorly they are very wide and very 

 sinuous ; their external openings are situated near together 

 at the posterior extremity. The excretory vessels in general 

 have a wall consisting of a thin layer of fibrillated proto- 

 plasmic material ; but in the scolex and neck region the four 

 main vessels have a fairly thick layer of longitudinal muscular 

 fibres. 



lieproducti ve Organs. 



The reproductive system will ])c best described lirst as it 

 appears in its fully developed coiulitiou in the free pro- 

 glottides. 



The testis (fig. 3, te.) consists of numerous rounded lobes 

 extending from the neck to behind the genital aperture. 



