MAMMALIAN CESTODES. 11 
with very muscular walls, in addition to a much larger ventral 
vessel. These are shown of the correct relative size in text-fig. 6, 
d.v.& v.v. The branches of the ventral trunk which connect the 
two ventral vessels of opposite sides of the body open as I have 
described in the older worm, by two branches into the ventral 
vessel. The transverse trunk traverses the bladder-cavity and is 
surrounded on its transit by a layer of tissue which here, as else- 
where, shows the commencing obliteration of the bladder-cavity. 
In this worm the longitudinal and transverse muscular layers of 
the body were very evident, and the worm was much pervaded by 
caleareous corpuscles. The latter were often grouped a few 
together in sacs not far below the subcuticular lay er. I shall recur 
to these in considering the structure of 
§ The Fully-developed Plerocercoid. 
In my former paper upon Urocystidiwm I gave some account of 
the general structure of the sexless worm which bears the buds. 
I have now a few additional remarks to make upon this stage. 
Text-fig. 7 represents a portion of a cross section to illustrate 
the inclusion of groups of calcareous corpuscles in cavities below 
the subeuticular layer. The corpuscles contained within are both 
larger and smaller, and there is also some granular detritus. The 
cavities themselves are rather elongated, but are always separated 
by muscular fibres running between them and at right angles to 
the longitudinal axis of the worm’s body. I have not studied the 
development of these cavities. I refer to them for two reasons. 
In the first place, the existence of quite similar agglomerations of 
calcareous corpuscles in the younger plerocercoid is one of the 
arguments which lead me to regard the various stages which I 
am now describing as being actual stages in the development of 
this worm—as for ming a true sequence in the order which I have 
indicated. In the second place, these saes of calcareous bodies 
are to be compared, as I believe, to apparently similar structures 
recently described by Prof. J. P. Hill*. The figure’ given by 
that author agrees very closely with that appended to the present 
paper (text- fig. 7), and the worm with which he deals is a 
Piestocystis stage, which thus agrees with the present species in 
some other particulars, though, as already stated, I cannot 
definitely refer the asexual stage to the Piestocystis type. The - 
investigation of the younger worms allows of an explanation of 
certain structural peculiarities in the older worm which I was 
unable to understand while preparing my former paper. There 
is, I think, no doubt that the central cavity is, as I then suspected, 
an extension forward of the cavity of the bladder, which we now 
know to be not limited to one dilated end of the body in the, 
young of this species of tapeworm. The elongated worm-like 
* * A Contribution to a further know ledge of the Cystic Cestodes.” Proc. Linn. 
Soc. N.S.W. (2) ix. p. 60. 
+ Ibid. pl. iii. fig. 6 
