T. B. ROSSETER ON THE ANATOMY OF DICRANOTmNIA CORONULA. 359 



longitudinal muscles of the neck and strobila, yet anastomose 

 with these longitudinal muscles at the base of the cyst. 



The protractor muscles (Fig. 1 c), are a series of muscular 

 fascicles placed equidistantly on the upper periphery or base of 

 the bulb, at the back of the circlet or crown of hooks. Each 

 fascicle is composed of numerous fine elastic fibres which form 

 a cone in the centre of the annule or orifice of the cavity. From 

 the endoderm of the zonal periphery of the orifice springs a 

 plexus of muscle fibres (Fig. 1 a), each one coalescing with the 

 fascicles of protractor muscles either at, or in close proximity 

 to, their apex. These angular protractor muscles, together with 

 the plexus, are only discernible when the rostellum is deeply 

 inverted within the cavity,* when the fascicles are stretched to 

 their fullest tension, and the plexus too has a downward acute 

 angle. On the eversion of the rostellum with its bulb, the 

 tension of these fascicles of protractor muscles is completely 

 relaxed ; and the rostellum, on emerging from the orifice, draws 

 up the plexus over its bulb, where, in prepared specimens, these 

 muscles are then seen coursing down longitudinally between 

 the interspaces of the hooks. 



The disassociation of the suckers by maceration enables us to 

 trace those muscles which elevate or depress them, so as to fix 

 or detach the scolex to the mucous membrane of the intestine. 

 From the back of the suckers, these muscles in a radiate form 

 pass through the surrounding tissue, and are attached in the 

 upper third in the region of the orifice to the ectothelial cuticle 

 of the rostellum cyst ; and thus their contractility, and expansion, 

 or in other words their fixative power, is subservient to the 

 retractor and protractor muscles. 



The structural composition of the Strobila is of a very complex 

 character, and this complexity increases in density by the growth 

 of the proglottis, thus obscuring, and rendering somewhat un- 

 definable, the generative organs as they approach maturity. This 

 structural density also increases the tenacity of the proglottis 

 when it becomes a uterine sac for the protection and development 

 of the oncospheres. Each sexual proglottis is composed cf 1st, a 

 cuticle 0'005 mm. thick, — this is, according to Linstow, 0-0028 mm. 

 in excess of the thickness of the cuticle of Tcenia dej^ressa ; 2nd, 



* It is usually inverted to a depth of O-O.'O ram. below the f-nnule or 

 orifice. 



