MAMMALIAN CESTODES. 21 
are in all the segments which I examined quite immature; but 
the cord of cells representing the future ducts were quite visible 
and were seen to lie always on the same side. This worm there- 
fore appears to have unilateral generative pores. This discovery 
renders the novelty of this worm as a genus rather more doubtful. 
But the facts now known do not permit of a settlement of the 
question. For the structure of the reproductive organs can alone, 
at the present day, determine the systematic position of these 
tapeworms. It is, as I think, unsafe to base generic identity 
upon other characters in the absence of information about the 
reproductive system. But it may be pointed out that there are 
undoubtedly certain resemblances in the structure of the water- 
vascular tubes of this worm and of Tenia crassicollis, which are 
mentioned above * in comparing the young of the two worms. 
But I do not think generic identity with Tenia proved. 
§ Summary and General Considerations. 
The fresh material reported upon in the foregoing pages 
enables me to define more fully the structure and life-history 
of the tapeworm which I described formerly as Urocystidium 
gemmiparum t, from Fiber zibethicus. 
As for the general structure of the fully grown asexual genera- 
tion I have nothing to add to my former description, to which 
reference may be made. The individual, however, which I have 
described and figured in the present paper, differs from that 
previously described in showing no development of buds. Two 
earlier stages in the development of the asexual worm are 
described in the present paper. ‘These are plump, short, but still 
vermiform, and segmented, worms. ‘They differ from the full- 
grown asexual worm: in the greater proportionate size of the 
bladder-cavity and other cavities perhaps connected with the 
bladder-cavity. But all of these cavities persist in the full-grown 
asexual stage. ‘They show no hooks or recognisable scolex. In 
the earliest stage there is no differentiation of the body-wall into 
cortex and medulla; in the more advanced young there are 
but feeble traces of this differentiation, quite achieved in the 
completely formed asexual worm. 
The structure of the asexual worm as elucidated by the 
younger stages described in the present paper, shows that it is 
not referable exactly to any type of asexual tapeworm as yet 
described. In spite, however, of its external and internal (trans- 
verse water-vascular vessels) segmentation, it is essentially a 
bladder-worm, but, as it appears, without a scolex. In com- 
plication of structure and in details, this asexual stage is not 
far different from the sexual stage. The sexual worm, which 
occurs in the same cavities of the liver side by side with 
* Supra, p. 14. 
+ It is to be borne in mind as possible, but not at all probable, that the two 
sets of worms are of different species. 
