662 DAVID HILT TENNENT. 
Tue Tart oF BUCEPHALUS. 
Ziegler’s description of the tail of B. polymorphus applies 
approximately to that of B.haimeanus. While my observa- 
tions agree in general with Ziegler’s careful description, and 
are, in fact, only supplementary to it, it is, perhaps, better to 
describe the structure in B. haimeanus rather than to 
merely consider the differences between the two forms. 
As already noted the tail consists of a middle piece, from 
each side of which is given off an appendage, the middle piece 
being in direct connection with the posterior end of the body 
(fig. 29). The basal portion of the middle piece has firm 
thickened walls whose structure is the same as that of the 
body wall. Posteriorly these walls pass out into a bladder- 
like structure, which is constricted in the middle, and laterally 
into the appendages. In the walls of this bladder, and on 
one side of the appendages, are seen in the living cercaria 
many clear, highly-refractive, spherical bodies. When stained 
these bodies become uniformly blackened, appearing to be 
solid, homogeneous structures. . 
In the appendages they extend in two definite rows 
(fig. 32), one on each side of the median line, from the base 
of the appendage to its tip (fig. 1). 
It seems probable that they are for the purpose of furnish- 
ing rigidity to the membranous portion of the middle piece 
and to the appendages. In the appendages they are so 
arranged that the compound rows become simple as the tails 
elongate. 
I was at first inclined to the view that they are the 
products of excretory activity. Similar structures have been 
noted in other T'rematode larve by various workers and their 
origin thus described. As I have not found them free in the 
lumen of the middle piece or of the appendages, but always 
apparently embedded in the wall, I am led to doubt my first 
impression, and to regard them as bodies formed for the 
purpose of support. Cells which may give rise to these 
