21 



backward parallel with each other (fig. 8), running upon the dorso-lateral parts of the 

 wide and straight alimentary canal. 



§ 5. Digestive System. — This system of organs includes a ' mouth,' with instruments for 

 seizing and comminuting the food, a ' gullet,' a ' stomach,' an ' intestine,' with vent and 

 accessory glands, of which, in the present genus, the ' liver ' only has been recognized. 



The mouth is median, and situated, as in other masticatory Crustacea, on the under 

 surface of the body ; it is, as in them, surrounded by modified portions of articulate limbs, 

 working laterally ; but these, in number and concentration, are parallelled only by the 

 extinct Merostonies (Cut, fig. 14, e. g.) : the mouth, it may be remembered, also resembles 

 that in Spiders in respect of its distance behind the fore border of the cephaletron (PL II. 

 fig. 2). The circumoral integument, in Linmlus, is yielding and elastic, cushioned out 

 with soft tissues, including fibres interlacing and susceptible, if muscular, of giving 

 change of form and position to the thick and prominent lips, endowing them with 

 movements, small in extent, but various, for seizing the morsels of food torn by the 

 haunch -palps or 'carders' (PL II A. p, p). The thick labial epithelium yields to 

 such movements by transverse folds or indents. The mouth opens on a plane not only 

 behind that of the basal attachment of the antennules (or ' first pair of chelate appen- 

 dages,' ii), but also clearly behind that of the basal attachments of the ' second pair,' or 

 antennse (iii). Nor can those of the ' third ' pair be said to be placed ' posterior to 

 the mouth.' Their nerves arise rather in advance than behind the oesophageal tube ; 

 and their haimches are on the transverse parallel of the anterior lip, as shown in 

 PL II A. fig. 1, n IV, & fig. 2, p IV. In a general way the mouth of Limulus may 

 be said to occupy the interspaces of the haunches {coxce) of the right and left limbs, 

 iii-vii, these limbs being crowded or close-packed at their basal articulations, on each 

 side of the mouth, whence they diverge to their pincer-shaped tips. The haunches are 

 compressed, as if squeezed together ; and their under or median borders are prodviced, 

 with a convex margin, which, with more or less of the contiguous flattened surface, is 

 beset with sharj:), short, slightly curved spines. These are not mere processes of the 

 chitine, bu.t are slightly movable, their base being articulated to a pit. The spiny plate, 

 or ' palp,' of the first of these jaw-feet (in) is inclined backward, and overlaps part of 

 that of the second (iv), which has a like relation to the third (v) ; this is set more 

 transversely, and is wedged, as it were, between the second and fourth. The haunch 

 of this foot (vi) has a similar position between that of the third (v) and the somewhat 

 less spiny haunch of the last pair of legs or ' masillipeds ' (vii). This complex series 

 or circle of carding-instrumeuts is bounded in front by the three- jointed antennse (ii), 

 having the same chelate structure as in the multiarticulate ones of Pterygotus (Cut, 

 fig. 14j) ; it is closed behind by the ' chilaria,' or pair of appendages marked * in Pis. II a. 

 &IV. 



The operation of these circumoral instruments in the living King-crab is thus described 

 by a close and accurate observer : — " The food is held immediately under the mouth by 

 the nippers of the anterior pair of feet (ii), aided, if necessary, by those of some of the 

 others. The manducatory limbs then begin an alternating motion of their haunches 

 upon the food, by drawing one of those rasp-like joints against the opposite one of the 



