io 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
to the body wall by two, or perhaps three, very slender bridles. The rectum is suspended 
by a broad sheet of tissue, stretching on each side to a point about midway between 
the anus and the nephridium. 
The oesophagus exhibits no contractile tubules. 
The body cavity is filled with eggs in one specimen opened, and these fill the 
nephridia also. These organs are of a pale pinkish colour, and owing to different degrees 
of contraction, the two organs differ in shape and size. One reaches back to the level 
of the origin of the dorsal retractor muscle, the other extends further back. 
Of the two pairs of retractor muscles, the ventral originates about 9 mm., the 
dorsal at a point 2 mm. from the anus. 
I give below a table showing the relative positions of these muscles, from which 
it appears that generally the ventral retractors are attached to the body wall at about 
halfway along the body, or in the posterior third of the body length; the dorsals at 
about one-sixth or one-eighth the length, measured from the anus. 
Distance from the anus of the attachment of the retractor muscles in P. mawsoni. 
Speci¬ 
men. 
Body 
length. - 
Ventral 
muscle. 
Dorsal 
muscle. 
Notes. 
M 
mm. 
17 
r? 
i 
3 
Hinder end flat; introvert withdrawn. 
N 
14 
9 
2 
Hinder end retracted. 
0 
14 
7 
2-5 
Terminal cone visible. 
F 
13 
ii 
3-5 
Hinder end retracted. 
Q 
11 
5-5 
2 
R 
10 
5 
2-5 
Localities .— 
Commonwealth Bay, 25 fathoms (3-4 ix 12) (forty-eight). 
Commonwealth Bay, 55-60 fathoms (21 xii 13) (three). 
Remarks— It is clearly distinct from P. margaritaceum and its varieties. It is 
true there are some resemblances between this species and P. georgianum 
where the hinder end of the body appears to bear a rounded knob, as in 
P. semperi. The skin is pale in colour, namely, “ silvery grey,” but it is 
also translucent and iridescent; moreover, the papillae are dark and are 
pear-shaped, while the internal structures show various differences. 
In P. charcoti Herubel, too, the colour is whitish, but the cylindrical 
papillae truncated terminally; the shorter introvert (less than half the body 
length), and the peculiar relations of the cerebral canal, mark it off from the 
rest as a very distinct species. 
