478 PROF. OWEN ON THE ANATOMY 
skeleton + is analogous to the tail-spine of the King-crab’s exoskeleton. The antecedent 
part of the thracetron (8”) wherewith the spine is articulated has no limbs. Is it also 
part of the pleon? and does the postganglionic part of the neural axis indicate the 
extent of such part ? 
In anatomizing, in 1843, my first-received specimens of Limulus, the details of the 
nervous system were followed out by my then anatomical assistant, Mr. Fioni Goadby, 
and well exemplify his peculiar skill and patience. 
$5. Digestive System.—This system of organs includes a ‘mouth,’ with instruments for 
seizing and cómminuting 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 resembles that in Spiders in respect of its distance behind the fore 
border of the cephaletron (Pl. XXXVII. 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, endow- 
ing 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 the basal attachment of the antennules (or * first pair of chelate appen- 
dages, ir) but also clearly behind that of the basal attachments of the * second pair,’ or 
antenne (111). 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 cesophageal tube; 
and their haunches are on the transverse parallel of the anterior lip, as shown in 
Pl. XXXVII. fig. 1, n 1v, & fig. 2, piv. In a general way the mouth of Limulus may 
be said to occupy the interspaces of the haunches (core) of the right and left limbs, 
II—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 movable, their base being articulated to a pit. The spiny plate, 
or *palp, of the first of these jaw-feet (111) is inclined backward, and overlaps part of 
that of the second (1v), 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 (v1), has a similar position between that of the third (v) and the somewhat 
less spiny haunch of the last pair of legs or * maxillipeds' (vir). This complex series 
or circle of carding-instruments is bounded in front by the three-jointed antenne (11), 
having the same chelate structure as in the multiarticulate ones of Pterygotus ; it is closed 
behind by the * chilaria,’ or pair of appendages marked * in Pls. XXXVII. € XXXVIII. 
The operation of these cireumoral instruments in the living King-crab is thus described 
by a close and accurate observer :—“ The food is held immediately under the mouth by 
+ Owen, * Anatomy of Vertebrates, vol. i. p. 49, fig. 44 c. 
