229 



ON HYMENOLEPIS FRAGILIS. 



By T. B. Rosseter, F.R.M.S. 



{Read January nth, 1908.) 



Plate 18. 



Taenia fragilis, n. sp., Krabbe, 1867. 

 Hymenolepis fragilis, Rosseter, 1906. 



In the year 1867 Krabbe took this tape-worm from the intestine 

 of the Teal (A?ias crecca, Linn.), commensal with T. malleus ; 

 and in his Bidrag til Kundskab, No. 57, p. 300, PI. 7, figs. 158- 

 160, describes it thus : 



Long. 40 mm. ; lat. 1*3 mm. 



Uncinulorum 8, corona simplex quorum, long. 0'056--059 mm. 



Aperturae genitalium secundae. 



Long, penis - 13 mm. ; lat. 0*004 mm. 



Habitaculum Anas crecca, in insula Foehr (Krabbe). 



I took this tape-worm from the intestine of a Wild Duck 

 (Anas boschas, /era, Linn.), and this is the only recorded instance 

 of its having been found since Krabbe discovered the species and 

 gave it the name of Taenia fragilis. 



Some difficulty is experienced, so far as the hooks of the 

 rostellum are concerned, in defining and determining the species 

 of either this tape-worm or that of Rudolphi's T. fasciata, as in 

 each instance the rostellum bears a crown of eight sickle-shaped 

 hocks. I have a few young specimens of T. fasciata with scolex 

 bearing eight hooks taken from Anas boschas, dom., fed by me with 

 cysticeroids of the same. To a critical eye the hook of T. fasciata 

 (PI. 18, Fig. 14) is more deeply curved than that of H. fragilis 

 (Fig. 13), whilst the root of H. fragilis is more thickened at its 

 proximal end than that of T. fasciata, and is also somewhat 

 hooked at its distal end. Then, again, if a single male or herma- 

 phroditic segment of H. fragilis were taken from the faecal 

 matter it would require a previous knowledge of the strobila of 

 T. sinuosa to discriminate accurately that the segment was not a 

 proglottis of the latter species, because H. fragilis has a spinous 

 bulb in the same locality of the proglottis as that of T. sinuosa. 



Personally I am placed in this position, Amongst my numerous 



