PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 201 



and XXXVI) is here confirmed by traces of external persistent segmentation in the 

 'telson ' of an ancestral type, dating back to the " Lower Old Red " period. — H.W.] 



§ 3. 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 recognised. 



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

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

 limbs, working laterally, but resembles that in Spiders in respect of its distance behind 

 the fore border of the cephaletron (PL XXXIV, fig. 2). The circumoral integument 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' (ib., 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 a basal attachment of the antennules (or ' first pair of 

 chelate appendages,' ii), but also clearly behind that of the basal attachments of the 

 'second pair' or antennas (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 oesopha- 

 geal tube ; and their haunches are on the transverse parallel of the anterior lip, as shown 

 in PI. XXXIV, fig. 1, n iv, and fig. 2, p iv. In a general way the mouth of Limulus 

 may be said to occupy the interspaces of the haunches {coxa) 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 produced 

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

 beset with sharp, short, slightly curved spines. These are not mere processes of the 

 chitine, but are slightly moveable, their base being articulated to a pit. The spiny 

 plate, or ' palp,' of the first of these jaw-feet (iii) 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 ' maxillipeds ' (vii). This complete series or circle 

 of carding instruments is bounded in front by the three-jointed antennae (ii), having the 

 same chelate structure as in the multiarticulate ones of Pteryyotus ; it is closed behind 

 by the ' chilaria ' or pair of appendages " marked * in Pis. XXXIV and XXXV. 



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

 described by the Rev. Samuel Lockwood, Ph.D., a close and accurate observer of its habits 

 (see the ' American Naturalist,' vol. iv, p. 260) : 



