io 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
for we find in some specimens witli the introvert fully extended or fully 
withdrawn that the hinder end is sometimes rounded and sometimes pointed; 
in the former case the longitudinal muscles are, of course, in a state of 
contraction, while in the latter they are relaxed. 
It follows, therefore, that the proportion of length of introvert to 
length of body is a variable, depending on the state of the worm at death, 
even if the introvert be fully extended, as some of the measurements given 
below will indicate, as do also those given by Lanchester. 
In measuring the length of introvert I have taken the anus as its 
base; Lanchester and Michaelsen use the nephridiopores, whereas Southern 
uses the anus, and it appears that Selenka takes this point also. I find the 
anus more useful, since the nephridiopores are not so easily detected, and, 
anyhow, they are only a millimetre or so in front of that aperture, so that 
the difference cannot be material. 
The only work in which a definite statement is made as to the extent 
of the introvert as a morphological feature is Delage and Herouard’s 
“ Zoologie Concrete ” (tome V, p. 12), where the anus is taken as marking 
the limit between the two regions. 
Now, although the worms above described are ascribed to the variety 
capsiforme, yet a comparison of measurements shows that the proportion 
of length of introvert to length of body differs from that given for the species 
and for this variety by various authors. 
The dimensions of the five worms are given below. The length is 
/ taken along the mid-dorsal line and not along the outer curve, if the worm 
is ‘curved, as so often happens. 
The largest specimen has the introvert only partially extended, and 
this is curved over to the right side and the apex bent backward. The total 
length along this outer curve is 200 mm., but along the mid-dorsal line it is 
160 mm. The greatest diameter of the body is 25 mm., and that of the introvert 
5 mm. The anus is situated 80 mm. from the hinder end on a brown papilla. 
Anteriorly to the anus the diameter of the body begins to decrease, and this 
slenderer region is 80 mm. in length. Its oral end is, however, withdrawal, 
and on slitting open the introvert it is seen that this internal portion 
measures 10 mm. and is much contracted, so that during life it would no 
doubt be much longer. 
Only one individual (from Station 1) has the introvert fully extended 
so as to show the tentacles;, the total length is 48 mm. and the anus is just 
halfway along this length, so that the introvert is equal to the body length. 
