208 ARTHUR E. SHIPLEY. 
the absence of hooks and introvert sheath, &c., the anterior 
part of the body which I have called the head is as unlike the 
typical introvert as possible, still in its relation to the lemnisci 
and to the ligament it occupies the position of that organ, 
and until we can get further information I think the best 
plan is to regard this part of the body as equivalent to the 
eversible part of more normal forms. 
The second of the three regions into which the body is 
externally divided is shorter than the head and smaller in 
diameter; it may be termed the collar. The third or poste- 
rior region, which may be called the trunk, is the longest and 
the most slender of the three; behind it tapers to a point 
where the orifice of the genital duct is situated, and this 
end of the animal is always a little turned up (figs. 1, 0, 11, 
and vit). The exterior of the collar and trunk are smooth 
or lightly wrinkled, but the head is covered with a number of 
small depressions or pits which give it a very characteristic 
appearance, and which are well seen in sections. The head is 
attached to the collar by a narrow neck, which is surrounded 
and concealed by the edge of the collar. It is obvious in 
sections (figs. v and x11). All the specimens were somewhat 
shrivelled and apparently distorted. The largest measured 
3°5 mm. in length, the smallest 2°> mm.; had they been fully 
distended they would probably have been 1 to 1:5 mm. longer. 
The body-cavity of the head is continuous with that of the 
neck, and the latter opens freely into the cavity of the trunk 
(fig. 13). The first-named space is by far the largest. The 
lumen of the collar region is reduced by the great thickness of 
the walls of this part of the body, and both here and in the 
trunk much of the internal space is occupied by the lemnisci 
and the reproductive organs. 
The skin is one of the most characteristic features of the 
Acanthocephala, and as far as I know is only paralleled by 
that of the Nematodes, but it possesses certain features not 
found in the last named group. The whole body is covered by 
a thin cuticle which does not vary much in thickness in the 
different regions of the body, and which is invaginated a short 
