308 T. B. ROSSETER ON CYSTICERCUS VENUSTA. 



more especially the construction and formation of the genital 

 organs. My object is to establish the species ; I shall therefore 

 confine myself to what I consider is of more vital interest in 

 proving the identity of this tape-worm with the Cysticercus, 

 and the specific character of the Taenia itself. I feel sure it 

 will facilitate reference and assist criticism if, before I pass 

 on to my opinions and enunciate my views, I place before you 

 in a tabulated form the measurement of these hooks as I 

 found them, both in the Cysticercoid stage in the body 

 cavity of the Cypris; and when as prehensile organs of the 

 mature tape- worm, in the intestine of the duck. In both 

 cases the number of hooks on the rostrum is eight (Fig. Id). 



Hook of Cysticercus, a-b, 0*024 ; a-c, 0'051 mm. 

 ,, „ Tape-worm, a-b, 0024 ; a-c, O'Ool mm. 



Here then we have demonstrable proof that these hooks, ac- 

 cording to measurement, are identical ; but this would scarcely 

 be sufficient evidence to rely on if it .were not for the f act- 

 that these hooks are the fac-simile of each other in their for- 

 mation. If Figs. 3 and 4 are compared, it will readily be 

 conceded that these two hooks are identically the same in both 

 these stages of the life-history of the creature ; and not only 

 do these hooks correspond with each other, but so also does the 

 rostellum, which in the adult or perfect scolex still maintains 

 its characteristic club-shaped, annulated formation, which I 

 have mentioned above in describing the Cysticercus. 



Having thus demonstrated that this Cysticercus and tape- 

 worm are identical, and that the Taenia from the drake is the 

 perfected scolex of the Cysticercus from Gorstly Wood Pond, 

 I shall now proceed to compare and contrast this tape- worm 

 with those Taeniae whose rostrum bears eight hooks, but it 

 must be borne in mind that the conclusions arrived at in 

 connection with the hooks of this tape-worm apply also to the 

 hooks of the Cysticercus. 



There are, according to Krabbe, 165 species of tape-worms 

 parasitic in birds, and of this number, less the one I am 

 describing, there are only six whose rostellum bears eight 

 hooks, and of these six up to the present time we are only 

 acquainted with the Cysticerci of two, viz., C. gracilis (Von 

 Linstow) and O. fascial a (Mavazek). 



