M2 
SUPPLEMENT 
jaws, so that the nutritive fluids may be extracted. Besides, 
we know that the scorpions, though without perforated man- 
dibles, nevertheless suck their prey in the same manner. 
The feet, in their relative size, vary, according to the dif- 
ferent positions, habitual to these animals, and sometimes 
even according to the sexes. They are inserted all around the 
sides of the chest, and composed of seven articulations. The 
last two constitute the tarsi, which are terminated by two 
hooks. It is easy to conceive that these two hooks answer 
the purpose to the arachnides of holding by their web, and 
that they must also be useful in its construction. 
The spinning epeirm are the only animals of this family that 
have the abdomen covered with a crustaceous or solid dermis, 
folded in the form of a ring. In all the other species this part 
of the body is soft, and without any apparent division. Its 
envelope is only a sort of sac, in which the organs of circula- 
tion, of respiration, the intestines, the vessels that secrete the 
silk, and in the females the ovaries, and the other sexual parts, 
are enclosed. Immediately under the dermis, the mucous 
tissue is perceptible, composed of a soft matter, divided into 
an infinite number of small grains. The heart is a large 
vessel along the back, throwing out branches on each side. 
The respiratory organs are two in number, and composed of 
small lamina?, adherent to the interior parietes of two pouches 
situated one at each side, near the base of the belly, and 
covered by a membranaceous lid, leaving a transverse cleft, 
for the passage of air. The place of these organs is usually 
indicated by two yellow or whitish spots. 
The intestinal canal is straight. There is a first stomach, 
composed of several sacs ; then, towards the middle of the ab- 
domen, is a second stomachal dilatation, surrounded by the 
liver. The silk-vessels, usually six in number, extend, on each 
side, along the whole interior : they resemble tortuous intes- 
tines, filled with a yellowish matter ; contracted rather abruptly 
