xv ANATOMY 40s 
that point. Immediately afterwards it dilates into a flask-like 
gastric sac which occupies almost the whole width of the abdomen, 
and proceeds straight to the anus. Viewed from above, the shape 
of this sac is entirely concealed by the large number of caeca 
(thirty) to which it gives rise dorsally and laterally. The two 
largest of these caeca extend, parallel to each other, over the 
whole of the abdominal portion of the gastric sac,and are flanked 
by four lateral pairs of smaller caeca, while there is a cluster of 
small caeca covering the anterior and narrower portion of the 
flask-like stomach. 
The large hepatic mass so conspicuous on opening dorsally 
the abdomen of a Spider is here entirely absent, but its functions 
are believed to be performed by certain wrinkled, tubular, longi- 
tudinally parallel bodies, about seven in number, closely applied 
to the wnder surface of the flask. 
The masticating portions of the maxillae of the pedipalpi and 
the first pair of legs are hollow distensible sacs, often seen in a 
swollen condition in specimens kept in spirits. They are 
furnished, on the inner surface, with a horny ridge. 
Owing to the fixity of the coxae of the legs, their maxillary 
plates are incapable of much lateral motion, but are rubbed 
against each other vertically. 
Beyond the fact that the heart is a dorsal tube lying along 
the anterior two-thirds of the alimentary canal, and divided by 
constrictions into three well-marked and equal portions, little is 
known of the blood-system of these animals. It is probably 
essentially like that of Spiders, but the presence of a pericardial 
sac has not yet been established, nor has the course of the blood- 
vessels been described in detail. 
As in other Arachnids, the principal ganglionic nerve masses 
closely embrace the oesophagus. Immediately anterior to it, 
forming a conical mass with its base on the oesophagus, is the 
cerebral ganglion, while just behind it is the transverse portion 
of the large thoracic nerve-centre. In Phalangium opilio, accord- 
ing to Tulk,! a median nerve is given off from the apex of the 
cerebral mass (the paired nature of which is apparent) and bifur- 
cates to the two eyes. Two lateral nerves proceed to certain 
organs near the origin of the second pair of legs, which were 
thought by the old writers to be lateral eyes, but which are now 
1 Mag. Nat. Hist. (i.), xii., 1845, p. 325. 
