FORM AND SIZE OF THE HEAD AND HOOKS. 



587 



the possession of a somewhat prominent crown (0*13 mm. broad) 

 which surrounds the bulging rostellum. The hooks borne by the 

 rostellum form, as in the other cystic tape-worms, two series of from 



FIG. 316. Adult Tcenia 

 echinococcus. (x 12.) 



FIG. 317. Echinococcus veterinorum (nat. size and 

 position). 



fourteen to twenty-five each, but they are rarely found in a perfect 

 state. The hooks are characterised by the thickness and solidity of 

 their roots (Fig. 315, <?). In details they vary widely even in the 

 same worm. 



Those of the inner series are, as usual, the larger, and when full- 

 grown attain a length of 0*04 to 0*045 mm. More than half of this 

 is formed by the roots ; the distance of the point of the anterior root 

 from the posterior end is 0*025 to 0*028 mm., and from the anterior 

 end only 0*017 to 0*019 mm. The claw is slender, and somewhat 

 strongly curved. The roots appear somewhat thicker and stouter, 

 inasmuch as the saddle-like notch between them is often more or less 

 completely filled up. The back of the posterior root not unfrequently 

 shows in the middle a shallow, curved cleft. The hooks of the second 

 series are not only smaller (0*030 to 0'038 mm. long), but have a 

 thinner posterior root, compared with which the markedly projecting 

 anterior root has an almost discoidal form. The distance of the end of 



