Variation in Hooks of Dog-Tapeworms 15 



Rostellum short, armed with a double crown of 26 to 32 hooks ; 

 large hooks (inner row) 139 to 175 /a in length, small hooks 

 (outer row) 78 to 114 ^ in length. Uterus median with 20 to 

 25 lateral branches. 



Ventral root of small hooks bifid. Gravid segments narrower 

 than those of T. scrrata. Embryophore ovoid. 



Synonymy. — Because of its close resemblance to T. cocnurus, 

 T. scrialis was formerly confused with that species. Experi- 

 ments with its bladder-worm, Cocnurus scrialis, in the rabbit, by 

 French experimenters, confirmed its distinctness from T. cocn- 

 urus, and it was classed as a distinct species by Baillet in 1863. 



For the sake of comparison with T. scrialis, the diagnosis of 

 T. cocnurus is given. 



Species T. cocnurus. Diagnosis. Taenia: Strobila 40 to 60 

 cm. in length ; head pyriform, 0.8 mm. in diameter. Rostellum 

 short, armed with a double crown of 22 to 32 hooks ; small hooks 

 (outer row) 90 to 130^ in length; large hooks (inner row) 150 

 to to 170 ix long. 



Ventral root of small hooks not bifid. Gravid segments broader 

 than those of T. scrialis. Embryophore spherical. 



Synonymy. — T. cocnurus Kiichenmeister 1853; T. (Cysto- 

 taenid) cocnurus Leuckart 1853. 



hooks of T. scrrata and T. scrialis 



Examination of a large number of these hooks shows a marked 

 variation in different particulars. There is not only a variation 

 in the number of hooks found on the individual heads of the same 

 species, but the hooks of the same and different heads of that 

 species differ from one another in size, general conformation, 

 and mutual relation of parts. 



In comparison of the hooks, each species is considered sep- 

 arately. There is such an extreme deviation in the comparative 

 magnitudes of the hooks of T. scrrata and those of T. scrialis, 

 that detailed differences need not be noted in distinguishing be- 

 tween the two species. As these hooks approximate very closely 

 in some characteristics the hooks of certain allied cestodes, it is 

 necessary to obtain a definite and exact description of the T. 



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