126 



THE CESTOIDEA 



distinctly and markedly constricted from the "neck" (Fig. XIX.). 

 The head stalk carries the " head," which is nearly square ; the 



1 



FIG. XIX. 



l.Tetrarhynchus (RhynchobotJiriuiri) hispidus, Lint., out of Trygon centrum. Entire strobila 

 (X circa 45, after Linton). A, the long scolex; B, the "body" consisting of five proglottids, 

 the last of which is nearly mature, a, one of the two phyllidia, formed by the fusion of a pair ; 

 it bears a single bothridium ; b, one of the four spiniferous proboscides ; c, the membranous 

 proboscis sheath ; d, the muscular bulb ; e, the "head stalk" ; /, genital pore. 



2. T. (Syndesmobothriurii) gracilis, Wagn., out of a cyst in Orthagoriseus mola (x 4J, orig., 

 from a specimen in the Oxford University Museum). The scolex had not separated from the 

 "bladder," a small portion of which is represented, a, one of the four independent and dis- 

 tinct bothridia ; b, one of the four proboscides. 



3. A portion of a proboscis of Tetrarhynchus, sp., out of the intestine of Carcharias(x 90, 

 orig.). The two kinds of hooks and their spiral arrangement are shown. 



4. Diagrammatic longitudinal section of a quadrant of a scolex, showing one bothridium, 

 and one proboscis which is partially everted, a, Bothridium ; b, proboscis ; c, proboscis sheath, 

 its cavity is shaded ; d, muscular bulb, with its cavity shaded ; g, retractor muscle ; /*, the 

 aperture in the scolex, through which the proboscis is everted, and to the margin of which the 

 membranous sheath is attached ; i, retractor muscles of the bothridium, inserted in the pro- 

 boscis sheath. 



