STUDIES ON THE TURBELLARIA. 443 
wards, like the bodies in the wall of the mouth-piece itself. It 
is these crescent-shaped bodies, I apprehend, that are referred 
to by von Graff (15) as gland-cells, and that are also noticed 
by Mark (20) in Polycherus. One end of each of these, 
the broader, becomes much more strongly stained than the 
rest, and this appearance may have led to the supposition that 
the bodies in question are of the nature of cells. ‘The narrower 
end is continuous with a fibre or fibres, which pass outwards 
into the substance of the bulb. It seems to me that the 
presence of these chitinous bodies in the interior of the bulb, 
with the fibre-like strands passing out from them, points 
directly to the conclusion that the bulb is composed of cells 
which, originally, like those forming the investment of the 
mouth-piece, have lost, for the most part, their secreting 
power, and have coalesced and become vacuolated to receive 
the sperms. 
The free extremities of the mouth-pieces extend far beyond 
the wall of the bursa. ‘Towards the extreme point, where the 
chitinous bodies become discontinued, the slender canal loses 
all traces of sheath, and terminates in the parenchyma, near 
the ventral surface of the body, in close proximity to the 
posterior extremity of the ovary and the ripe ova. In several 
specimens I was able to sce sperms issuing from the end of 
the canal, and wandering out into the surrounding paren- 
chyma. 
In number and arrangement the chitinous mouth-pieces are 
very irregular. Most commonly there are four in each bursa ; 
but in some cases there were only two, and in others as many 
as nine. Very often the number in the two burse is unequal. 
In one specimen the entire bursa was duplicated on one side, 
though not on the other. Often a bulb, or more than one, 
has no mouth-piece. Nearly always two of the bulbs are 
partially fused. Very frequently one or more of the mouth- 
pieces are incomplete—the basal part, usually, being absent,— 
as if in course of absorption or regeneration. 
The parts just described, namely, those known as burse 
seminales, with their chitinous mouth-pieces, are very im- 
