212 ARTHUR E. SHIPLEY. 
In the more typical Acanthocephala the anterior end of the 
body terminates in a hollow eversible portion provided with 
rows of hooks whose number and shape have a certain sys- 
tematic value. This introvert can be withdrawn, not into the 
general body cavity, but into the cavity of the introvert sheath, 
which is shut off from the general body cavity by a double 
(chinorhynchide) or a single (Neorhynchidz) wall. The ex- 
trusion of the introvert is believed to be effected by fluid being 
forced into its lacunze by the lemnisci. It is retracted by 
special muscles attached to the inside of its tip; besides these, 
other retractor muscles run from the outside of the introvert 
sheath, and these serve to retract the whole sheath and its 
contents into the trunk. The chief nerve ganglion lies as a 
rule on the posterior end of the introvert sheath, usually in 
the middle line, but in the Gigantorhynchidz it is placed to 
one side. From the posterior end of the introvert sheath, and 
having its origin between its two walls when they are present, 
the ligament runs backward, traversing the body cavity, and 
ending in the funnel-shaped internal opening of the oviduct in 
the female and in the vas deferens in the male. 
Owing to the absence of an introvert and its sheath, the 
relations of the ligament in the present species is somewhat 
altered. It takes its origin from the anterior end of the head, 
and at first seems to consist of a few strands of muscular 
fibres which arise from the muscles of the skin (fig. x1). All 
my specimens but one proved to be mature females, whose 
ovaries had broken up into the egg masses which are character- 
istic of the Acanthocephala. These egg masses consist of 
packets of a dozen or more cells of which the peripheral layer 
develop into ova at the cost of the central cells which serve 
them as a food supply (figs. v1, x1, and x11). These packets 
coexisted in my specimens with ova in various stages of 
development, some without any egg shell, whilst others were 
provided with a thick deeply-staining membrane. The whole 
lumen of the head was crowded with these ova. In the region 
of the collar the ova were confined by a thin-walled membrane, 
and in the trunk there were two such masses of ova, which, 
