514 
PYCNOGONIDA CHAE: 
gnathites. The mouth, situated at its apex, is a three-sided 
orifice, formed by a dorsal’ and two lateral lobes; and hence the 
\Z--L 
S ep) (6 
N’ =-1___ 
Fie. 277.— Longitudinal 
section through one 
“‘antimere”’ of -the 
proboscis in Phoxi- 
chilus charybdaeus. 
G, g', Principal and 
secondary ganglia; h, 
sieve- hairs; JZ, lip; 
mt, oral tooth ; WV, NV’, 
inner and outer nerve- 
cords ; ¢, proboscis- 
teeth. (After Dohrn.) 
proboscis has been assumed by some, on 
no competent evidence, to be constituted 
of a degenerate “pair of appendages and 
a labrum or upper lp. Each of the 
three lobes which bounds the mouth 
shows the following structures: firstly, a 
lappet of external chitinised integument, 
overlapping, as the finger-nail overlaps 
the finger, a cushion-hke lp, ridged after 
the fashion of a fine-cut file in some 
species, hairy in others, on the inner surface 
where the three ips meet to close the orifice 
of the mouth. Below this again is a pro- 
minent tooth (Fig. 277, md), supported, as 
are the lips, by a system of chitinous rods, 
which are but little developed in the genus 
here figured, though conspicuous and com- 
plicated in others. Transverse ridges run 
across the angles where adjacent lips meet, 
and the whole mechanism constitutes an 
efficient valve, preventing the escape of 
swallowed food. The greater portion of the 
proboscis 1s occupied by a masticating or 
triturating apparatus, the oesophageal cavity 
expanding somewhat and having its walls 
densely covered, in three bands correspond- 
ing to the antimeres, with innumerable 
minute spines (i) or needles, sometimes 
supplemented by large teeth (7) that point forwards somewhat 
obliquely to the axis of the proboscis.” 
In the curious East Indian genus Pipetta (Loman) the sucking 
and sifting mechanism is low down in the proboscis, and the organ 
is prolonged into a very fine tube, the lips growing together till they 
leave an aperture of only ‘(007 mm. for the absorption of liquids. 
' The dorsal lobe is absent in Rhynchothorax. 
* For a very detailed account of this mechanism, here epitomised in the merest 
outline, and for an account of its modifications in diverse forms, the student must 
consult Dohrn’s Monograph (¢. cit. pp. 46-53). 
