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 



r^-'.l 



Fio. 316.— Adult Tcmia 

 echinocoocus. (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, C). 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 0019 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 (O'OSO to 0038 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 

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