358 T. B. EOSSETER ON THE ANATOMY OF DWRANOTmNIA CORONULA. 



or circlet of 18 to 24 (the latter is the more constant) pitchfork- 

 shaped hooks. The under or posterior root is blunted or club- 

 shaped, whilst the anterior is a short, sharply curved hook ; the 

 posterior root is 0*007 mm. long, and the whole length of the 

 hook is 0*013 mm. The anterior portion of these hooks in fresh 

 or well-preserved specimens stands boldly out from the periphery 

 of the crown at a right angle from the convexity of the bulb, 

 like spikes on a " cheval-de-frise," whilst the j)osterior root is 

 buried deeply in the muscular bulb. The bulb is 0*038 mm. long 

 and 0-088 mm. broad. It is composed of a dense mass of circular 

 and very fine longitudinal muscles. The apical portion of the 

 rostrum is a pyriform aggregated mass of cellular tissue, enclosed 

 by a structureless membrane, and encircled by a series of broad 

 retractor muscles ; the whole mass, inclusive of the bulb, being 

 0'074: mm. long. In a previous work on the scolex of this 

 tape-worm I stated that " there was no cavity, but that the 

 hard muscular bulb pressed down on invagination the paren- 

 chymatous tissue, etc." This is somewhat erroneous, for the 

 disassociation of the rostellum from the surrounding tissue by 

 maceration and teasing, and also by pressure under a cover- 

 glass, reveals its structural formation and mechanism. 



In the centre of the crown of the scolex is an orifice (Fig. 1 a), 

 which varies in its formation from a circle to an oval, according 

 as the scolex is contracted or expanded ; this leads into a deep 

 ovate cavity or cyst which is lined by an endothelial membrane, 

 its exterior being convex; it has a depth of 0169 mm. and its 

 equatorial diameter is O'lOl mm., and within this ovular cavity 

 or cyst, when inverted, is the rostellum with its bulb. It is held 

 in position in the centre of the cavity by its protractor and 

 retractor muscles, and also by a strong muscular elastic footstalk, 

 which is firmly attached to the membraneous lining at the basal 

 centre of the cavity; and thus it, the rostellum, is kept in a 

 concentric position within the cavity. 



The retractor muscles (Fig. 1 b) spring from the endothelial 

 wall of the lower third of the cavity. Spreading themselves over 

 the surface of the rostellum, they find their termination, or seat 

 of attachment, at the edge of the circlet or crown of hooks, close 

 under their posterior roots ; and on inversion they hang down 

 within the cavity, like a festoon of ribbons. These muscles, 

 although not performing the same functions as the broad 



