CHAP, XIII ARANEAE—SPIDERS 315 
and the number of known forms is certain to be very largely 
increased. They form an extremely compact and natural group, 
for though, within the order, there is an infinite variety of 
detail, their uniformity in essential points of structure is remark- 
able, and they are sharply marked off from the neighbouring 
groups of Arachnida. 
It is perhaps unfortunate that the cbtrusiveness of particularly 
unattractive specimens of the race has always caused spiders to 
be regarded with more or less aversion. 
This prejudice can hardly fail to be 
modified by a wider acquaintance with 
these animals. There are certainly 
few groups which present points of 
creater interest im respect to their 
adaptation to special modes of life and 
the ingenuity displayed in the con- 
struction of their nests and the en- 
snaring of their prey. 
Spiders are wingless, yet they may 
often be observed travelling through 
the air. They are air-breathing, yet 
many are amphibious in their habits, fre. 172.—Xpeira angulata. 2. 
and one species at least spends the 
ereater part of its existence beneath the surface of the water. 
On land they may be found in all imaginable localities which 
admit of the existence of that insect life on which they depend 
for food. 
External Structure——The spider’s body consists of two 
portions, the cephalothorax and the abdomen. 
Cephalothorax.—Looked at dorsally (Fig. 173), the cephalo- 
thorax is generally seen to have a depression near the middle, the 
“median fovea,” and from this certain lines, the “radial striae,” 
radiate towards the sides. These depressions indicate the attach- 
ment of internal muscles. 
The head region or “caput ” lies in front of the foremost of 
the radial striae, and is often clearly marked off from the thorax, 
and different from it in elevation. It bears the eyes, which, in 
the vreat majority of spiders, are eight in number. Many, how- 
ever, are six-eyed, while in rare eases the number is reduced to 
four (Tetrablemma, see p. 404), or even to two (Nops, see p. 395). 
