MAMMALIAN CESTODES. 7 
like earlier stages of this Gf I am right in so regarding them). 
It would appear, therefore, that the facts which have just been 
referred to in the structure of the bud may be perhaps really 
looked upon as arguments in favour of a comparison of the bud 
with the fully adult sexual form and a conclusion that the former 
ultimately gives rise to the latter. For if we are to assume that 
these buds give rise to the plerocercoid, it will have to be further 
assumed that the regularly arranged and perfectly differentiated 
cortex and medulla of the bud becomes lost, only to be recon- 
structed later when the plerocercoid has arrived at the completion 
of its development. Of the alternatives, this seems to me to be 
‘the less likely. In short, I am obliged to admit that the develop- 
ment of the bud into the sexual worm is mainly probable on 
account of the difficulties which beset the view that it is an earlier 
stage of the plerocercoid. 
$ The Sexual Form. 
The sexual form appears to differ in several particulars from 
that of my first specimen of Urocystidium gemmipavum*, and I 
have been able to compare the two placed side by side. It is to 
be noted, however, that they agree with each other in differing 
from the asexual worms in their browner colour. ‘This is perhaps 
rather more strongly marked in the individual which forms the 
subject of the present communication to the Society. 
In the case of both worms, the segmentation begins immediately 
after the scolex and the segments are quite narrow. ‘They get, 
however, slightly longer at the posterior end of the body, and in 
the new specimen the last three segments are comparatively long 
though not nearly so long as broad. The body ended abruptly 
with the last of these segments. The present worm contrasts 
with the original specimen in its smaller size; it is of about half 
the length, measuring some 42 mm., and is not nearly so broad, 
the greatest breadth being 4 mm. 
It is, however, in the scolex that the most prominent difference 
between the two individuals is to be found. Of this region I 
have had drawings prepared, which are shown in text-figure 8. 
On a superficial view, with a hand-lens only, the scolex of the 
second individual is seen to be much smaller than that of the 
specimen which I described a year ago. ‘This difference is 
heightened when the two are compared under a compound 
microscope. ‘The upper right-hand figure in the illustration 
(text-fig. 8C) shows that in the new specimen the scolex end is 
terminated by a thin collar, in which a row of sets are imbedded 
forming a complete circle. A good way below this are the 
suckers, which are relatively small and separated from the hooks 
. by a larger interval than that which occurs in the type example 
of Urocystidium gemnuiparum. It might perhaps be held that 
* Loc. cit. p. 841. 
Proc. Zoou, Soc.—1914, No, II. 
bo 
