DREPANIDOTAENIA TENUIROSTRIS. 401 



especially when we take into consideration how much depends, 

 in defining the species, on the formation, contour, size and 

 number of the hooks on the rostellum. The liooks of all three 

 of these species — viz. tenuirostj'is, longirostris, and sinuosa (I have a 

 specimen of each species in my cabinet) — have so many discrepancies 

 and are so dissimilar in respect to contour, formation, and size, 

 that one has no difficulty in defining and diagnosing either of 

 these species by the hooks of the rostellum. 



The tape-worm from which I have made the following obser- 

 vations is one I had produced by infecting ducks (Anas boschas 

 fZowi. ) with cysticercoids. It was 39 '400 mm. long ; was composed 

 of about 400 proglottides or segments, which gradually ^viden 

 from 0'084mm. to 1-5 mm. — which is their extreme breadth, from 

 each lateral border — in the uterine segments. It will thus be seen 

 that this specimen, although a mature worm, falls far short of 

 that of the Bremser-Kudolphi specimen, and is but |-th of that 

 of Krabbe. It was not what we call a virgin worm, because it 

 had already shed a portion of its strobila, which was composed 

 wholly of uterine segments. I have others in my collection, 

 which I took from the intestine of the same duck, in various 

 stages of growth, from the scolex, with its immature collum, the 

 result of late experimental feeding, to that which I have selected 

 for the production of this paper. 



Description of the Worm. 



The head or scolex is subglobose, 0*27 mm. wide and 0"135mm. 

 long. From the crown springs a long attenuated retractile 

 rostellum approximately 0*112 mm. long and 0*023 mm. in 

 diameter; it is terminated by a bulbous rostrum, around which 

 are arranged ten sickle -shaped hooks 23 fx long. At the base of 

 the rostellum, deeply sunk in the middle of the scolex, is a 

 muscular pyriform bulb or root (see Journ. Q. M. 6'., Ser. 2, 

 vol. vi.. No. 41., pp. 397-405, PI. XVIII., Figs. 9-11), which 

 sends a series of retractor muscle fibres to the rostrum. These 

 muscle fibres invert the rostrum, together with the hooks down 



