T. R. ROSSETER OX A NEW CYSI'ICERUS PROM CYCLOPS AGILIS. 181 



width of the cyst was 0*255 ra.m., and the long diameter 

 0-282 m.m. 



The hooks of the future rostrum were eight in number 

 (Fig. 4), including one which was malformed, that is to say, the 

 root was aborted. They formed a fascicle and lay obliquely in 

 the cyst. These hooks are the chief consideration in the 

 investigation of Cysticercoids. as from them alone is determined 

 the species of the mature form or tapeworm. In this instance 

 the extreme length of the hook from the posterior root to the 

 tip is 0*050 m.m., and is divisible thus : a to h 0*028, a to c 

 0*050 ; a to 6 being the length from the posterior to the anterior 

 root, and a to c the whole length of the hook. 



At present we are only acquainted with six species of Tcenia 

 infesting birds, whose rostra bear eight hooks. These are : — 



T tenia gracilis 0*077-0*080 m.m. 



„ ohvelata ... ... 0*076 m.m. 



„ fasciata ... ... 0*057 m.m. 



„ fragilis ... ... 0*056 m.m. 



,, octacantha... ... 0*036 m.m. 



,, lanceolata ... ... 0*031 m.m. 



For the sake of comparison of the length of the hook, we may 

 select from this list T. fasciata and T. fragilis as corresponding- 

 most nearly in size to the hooks of the Cysticercus under con- 

 sideration. The Cysticercus of T. fasciata is already known, 

 but that of T. fragilis is still undiscovered, and on reference to 

 Fig. 5, hook of T. fragilis, and Fig. 6, hook of Cysticercus (r), 

 it will at once be observed that there is no similarity between 

 them. 



From the table given below it will be clearly apparent that 



the length, both of the root and the barb, in either case, for 



there is great similarity between the hooks of T. fasciata and 



T. fragilis, is totally at variance with the one in question. 



(a-b 0*025 m.m. 

 Tcenia fragilis j 



fasciata 



(a-b 0*02, 

 \a-c 0-0d\ 



a-c 0*056 m.m. 

 '025 m.m. 

 '057 m.m. 



ra-6 0*028 m.m. 



Cysticercus . . . Cf) -j a.a-a 

 -^ ^ -' (^a-c OoO m.m. 



It is possible that the final host of this Cysticercus will be 



found to be either the domestic goose or duck. I am led to 



