310 T B. ROSSETER ON CYSTICERCUS VENUSTA. 



I will first consider and discuss the hooks of those tape- 

 worms whose Cysticercus is up to the present time un- 

 discovered. 



The hooks of T. lanceolata are, as will be seen by Fig. 6, 

 both in size and formation totally at variance with those of 

 this Taenia. The whole length is smaller by 0016 mm., and 

 the same objection applies also to T. octacantha (Fig. 7), which 

 is 0*015 mm. less. A casual observer of T. obvelata (Fig. 8) 

 might be disposed to think that there was, by the contour and 

 formation of this hook, some affinity between it and this Taenia, 

 but the objections applied to the two previous species apply 

 also, but in the opposite direction, to the hooks of T. obvelata, 

 which are 0025 mm. longer than those of this tape-worm, 

 consequently this is not the Cysticercus of either of these 

 species of Taenia. T. gracilis (Fig. 9), with its Cysticercus, 

 found by Von Linstow amongst debris of crustaceans in the 

 intestine of the perch, calls for but few remarks from me, 

 as its hooks, which measure in both instances 0077 mm.- 

 0*080, are not only in excess in length by at least 0*026 mm., 

 but the whole form of the hook is totally differeut in com- 

 parison with the hook of this Taenia, and the Cysticercus has 

 a distinguishing characteristic in connection with it, for, like 

 no other Cysticercus with which I am acquainted, the cuticle 

 of the cyst is indented towards the apex, or point of 

 invagination, which gives it the aspect of being gibbous. 



The two remaining Taeniae of this class are T fasciata (Fig. 

 10) ; whose Cysticercus was found by Mavazek in the body cavity 

 of Cyclops agilis, and T.fragilis (Fig. 11), whose Cysticercus is at 

 present undiscovered. I have taken these two Taeniae together 

 because, both in measurement and formation, there is a great 

 similarity between their hooks; but there are a few points in 

 which they differ, which are distinguishable, and enable us to 

 identify them. The hooks of the former measure, according to 

 Krabbe, 0*051 mm., the latter 0056-0*059 mm. My own measure- 

 ment, from specimens of the former in my cabinet, corroborates 

 that of Krabbe. T. fragilis I have not seen. On reference to 

 Table (page 309), it will be seen that the division of the hooks 

 from a-b and a-c are in both instances nearly alike ; but the 

 difference lies in the formation of the hook. In T. fasciata, 

 from a-b the point of the hook a is sharp, and gracefully sweeps 



