PYCNOGONIDA 



CHAP. 



gnathites. The mouth, situated at its apex, is a three-sided 

 orifice, formed by a dorsal l and two lateral lobes ; and hence the 

 proboscis has been assumed by some, on 

 no competent evidence, to be constituted 

 of a degenerate "pair of appendages and 

 a labrum or upper lip. 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-like lip, ridged after 

 the fashion of a fine -cut file in some 

 species, hairy in others, on the inner surface 

 where the three lips meet to close the orifice 

 of the mouth. Below this again is a pro- 

 minent tooth (Fig. 277, mt}, 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, 



FIG 277 Longitudinal anc ^ * ne whole mechanism constitutes an 



section through one efficient valve, preventing the escape of 



proioTdf in pJS- swallowed food. The greater portion of the 



chttu-s charybdaeus. proboscis is occupied by a masticating or 



G, g', Principal and . . , , , . 



secondary ganglia ; h, triturating apparatus, the oesophageal cavity 

 sieve - hairs ; L, lip ; expanding somewhat and having its walls 



mt, oral tooth ; J\\ X', 



inner and outer nerve- densely covered, in three bands correspond- 

 cords ; t, proboscis- j ng to ^he antimeres, with innumerable 



teeth. (After Dohrn.) 



minute spines (h) or needles, sometimes 

 supplemented by large teeth () that point forwards somewhat 

 obliquely to the axis of the proboscis. 2 



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. 



N \ 



1 The dorsal lobe is absent in Rhynchothorax. 



2 For a very detailed account of this mechanism, here epitomisei in the merest 

 outline, and for an account of its modifications in diverse forms, the student must 

 consult Dohrn's Monograph (t. cit. pp. 46-53). 



