29 ON MAMMALIAN CESTODES. 
the asexual stages, is of roughly the same size as the fully- 
developed asexual stage. It has a very strongly muscular 
rostellum and two rows of sixteen hooks each, the outer row 
consisting of smaller sized hooks than the inner. The body of the 
sexual worm is crammed with large oval calcareous bodies with a 
centrally placed nucleus. Such bodies are also very abundant, but 
not so abundant, in the bladder-worms. The gonads, etc. (quite 
immature in both individuals) are fairly central in the pro- 
glottids, and the ducts are all directed towards the same side of 
the body. 
It would appear, therefore, that both the structure of the 
immature tapeworm and the series of stages by which maturity 
is arrived at, are quite unlike anything that is at present known 
among the Cestoidea. But as there are obvious lacune in the 
information which has been set forth in the present paper, some 
uncertainty attaches to the life-history the course of which 
is suggested by those facts. There are, as it would appear, 
two larval stages following each other and derived from each 
other directly. From the egg (as I presume in the absence of 
earlier stages) arises the larva which I have described as a plero- 
cercoid ; this gives rise by budding to many larvee which differ in 
several structural features from the asexual parent; these (and 
here there are no positive facts but only inference) give rise to 
the sexual worm. ‘There are thus three stages in the life-history 
of this tapeworm which are not met with in other Cyclophyllidea, 
except as mere multiplication as in Hchinococcus. Bothriocephalus 
has three distinct stages, but they are not comparable to those 
described here, since the first is a free-swimming ciliated larva 
The complication of the life-history in this form is suggestive, 
of course, of the Trematoda; but I can make no detailed 
comparison. 
