388 
CLASS ARACHNID A. 
similar in form, but of various sizes, are composed of seven 
articulations, the first two of which form the haunches, the 
following the thigh, the fourth and fifth the leg, and the other 
two the tarsus. The last is terminated by two hooks, usually 
denticulated like a comb, and in many by an additional one, 
but smaller, and without denti dilations. The intestinal canal 
is straight : it consists of a first stomach, composed of several 
sacs, then towards the middle of the abdomen, a second 
stomachal dilatation surrounded with silk. According to the 
observations of JYI. Leon. Dufour (Annal. des Sc. Phys.tom.vi.), 
it occupies the greater portion of the abdominal cavity, and is 
immediately enveloped by the skin. It is of a pulpy con- 
sistence, formed of small grains, whose peculiar excretory 
ducts unite into many hepatic canals, pouring into the alimen- 
tary tube the product of the secretion. At the middle of its 
superior surface is a deep line, where the heart is lodged, and 
which divides this organ into two equal lobes. Its form varies 
like that of the abdomen, according to the species, thus its 
contour is festooned in the Epeira sericea . In this sub- 
genus, as well as in the Lycosa tarentula , its surface is 
covered with a coat of a chalky white, cut into areolae, which 
are easily perceived through the smooth skin of some species. 
They are observed to obey the motion of the systole and dias- 
tole of the heart. The individuals of both sexes often shoot 
through the anus an excrementitious fluid, composed of one 
part white as milk, and another black as ink. 
The nervous system is composed of a double cord, occupy- 
ing the medial line of the body, and of ganglia, which distri- 
bute nerves to the various organs. M. Dufour has been unable 
to determine the number and disposition of these ganglia; 
but, according to the figure which Treviranus has given of this 
system, the number of ganglia should be but two. The obser- 
vations of the latter also supply the deficiencies of M. Dufour, 
relatively to the organ of circulation, which, according to him, 
