MAMMALIAN CESTODES. 105} 
and the completely formed sexless worm; the metamorphosis 
is obviously a matter of gradual growth. The question next 
arises as to what is the relation of the complete plerocercoid to 
the adult tapeworm. Is the one converted into the other? To 
settle this matter, or rather to contribute to its settlement, we 
must again consider the buds produced by the sexless worm. 
But I shall first make a 
S Comparison of Immature Urocystidium (fully developed 
Plerocercoid) with Cysticercus fasciolaris. 
In my earlier paper upon this worm I compared these two 
forms in certain details; but the description was concerned with 
external characters alone. Now that I have been able to ascertain 
some more facts about the development of the asexual form, a 
more detailed comparison will be made. My information as to 
Cysticercus fasciolaris is chiefly derived from Bartels’s memoir 
cited below *. Although a primary difference of great importance 
absolutely separates the two immature forms, it is rather remark- 
able that the number of hooks in the Cysticercus fasciolaris seems 
to be identical with that of the sexually mature Urocystidiwm. 
Bartels gives 34-36 hooks, arranged, as they are in the present 
species, in two circles. But though this statement is made in 
the text, only 16 in one row are figured by him, and, moreover, 
in two different figures 7. This is the number that is met with 
in the adult Urocystidiwm. In the immature form, as I have 
mentioned, there is no trace of hooks that I could discover. In 
both forms the calcareous corpuscles are very numerous. But 
while in the present species these corpuscles are most numerous 
in the sexual form, the reverse is the case in Cysticercus fascio- 
laris, the mature worm, 7'@nia crassicollis, having fewer calcareous 
bodies. ‘The most noteworthy resemblance seems to me to lie in 
the disposition of the bladder of the two worms. In the Cysti- 
cercus the bladder is situated at one end of the body, and is very 
smal] compared with the freeand segmented portion of the worm. 
As I have already pointed out, precisely the same is the case with 
Urocystidiwm. But in both cases the cavities found in the worm 
are not limited to a restricted bladder. Cavities occur in both in 
the segmented part; these are in Cysticercus mainly limited to 
the posterior end of the body, but they are also found anteriorly ; 
so that there is here no essential difference from Uvrocystidium. 
Bartels remarks of these cavities that they are some of them con- 
nected with the bladder-cavity while others are cut off from it. 
He mentions that these cavities are sharply marked off from the 
parenchyma in which they lie, but that they cannot be said 
to possess definite walls. There is thus a greater resemblance to 
the bladder-cavity of the buds of Urocystidiwm than to that of 
* Zool. Jahrb. Bd. xxi. 1902, Abth. f. Anat. p. 511. 
+ Loe. cit. taf. 39. fig. 21 & taf: 38. fig. 15. 
