CHAP. XHI 



ARANEAE — SPIDERS 



315 



and the mmiber 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 rmiformity in essential points of structure is remark- 

 able, and they are sharply marked off from the neighbouring 

 grou.ps of Arachnida. 



It is perhaps unfortunate that the obtrusiveness 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 

 greater interest in 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, fig. 172.— Epeira anguiata. 9 . 

 and one species at least spends the 



greater 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 great majority of spiders, are eight in number. Many, how- 

 ever, are six-eyed, while in rare cases the number is reduced to 

 {our (TetraUemma, see p. 404), or even to two (iVbps, see p. 395). 



