AX ATOMY 01-' SPIDERS. 



167 



cephalothorax, which, in the Solpugidae the most Spider-like of the preceding families is divided into 

 four distinct rings, is here once more united into a single mass without segmentation ; the abdomen, 

 which also shows no division into segments, is attached to the back of the cephalothorax by a more or 

 less slender peduncle ; the cephalothorax has four pairs of limbs ; and the antennae are represented 

 by a pair of falces (chelicerae), which perform the part of mandibles, and have a movable, claw-like, 

 terminal joint. The respiration is performed by both lung-sacs and tracheae. 



The cephalothorax in these animals is covered above by a more or less horny plate, towai'ds the 

 front margin of which a group of simple eyes is situated. These are generally eight in number, but 

 sometimes only six, or even less, and their relative position is of considerable importance in the 

 determination of species and genera. The falces, which spring from the front of the cephalothorax 

 above the mouth, are generally bent down vertically, but sometimes project more or less forward. Each 

 of them consists of two joints, of which the basal one is large and stout, and furrowed along the inner 

 margin, while the second is claw-like, sharp, and articulated to the 

 apex of the first in such a manner that it can be folded back into 

 the groove of the latter, and when erected it forms a biting organ 

 more or less opposed to that of the opposite side. These may, in fact, 

 be regarded as the jaws of the Spider, and they are rendered for- 

 midable weapons by the circumstance that they are perforated, and 

 the canals passing through them to the apex of the claw-joint receive 

 the ducts coming from a pair of poison glands, consisting of blind 

 sacs, which extend more or less into the cephalothorax. The fluid 

 secreted by these glands is poured into the wounds inflicted by the 

 claws of the falces, and its effect upon the animal attacked is very 

 marked. 



As in the Arachnida generally, no mandibles are to be recog- 

 nised, but the maxillae are plainly developed, and bear a pair of 

 palpi consisting of several joints. In the females these are simple 

 organs like the legs, but shorter, and furnished with a claw at the 

 end ; in the males the last joint is inflated and excavated, and 

 usually furnished with peculiar appendages which are employed 

 in the transfer of the fertilising elements to the reproductive 

 organs of the female. The labium, or part of it, would appear 

 to be represented by a small piece projecting forward between the bases of the maxillae, which 

 is either joined to or separate from the sternal plate occupying the lower surface of the cephalo- 

 thorax, from the edges of which the limbs take their origin, the first pair, which, as we have already 

 seen, may be regarded as representing a second pair of palpi, as well as the rest. The legs consist of 

 the usual number of pieces a large coxa, a small trochanter, and a well-developed femur, followed by 

 a tibia of two pieces, and a tarsus also usually of two joints. At the extremity of the tarsus are two 

 claws, often associated with other organs which may be noticed under the families. The abdomen is 

 generally covered with a soft skin, and except in a few instances shows no indications of its being 

 originally composed of segments ; near the apex on the under side it bears two or three pairs of 

 spinnerets, to which we shall have to refer by-and-by. 



In their internal anatomy the Spiders conform to the type already described (pp. 158, 159), but 

 show certain special peculiarities. Thus the oesophagus has horny walls and terminates in a muscular 

 dilatation, attached by a strong muscle to the back of the cephalothorax an arrangement which 

 renders it an efficient suctorial apparatus. The stomach is furnished on each side with five blind 

 tubular extensions, which run towards and usually penetrate more or less into the palpi and legs ; and 

 the intestine continues tubular to near the extremity of the body, before reaching which it is 

 dilated into a somewhat globular rectum. All these parts are kept in place by the voluminous 

 lobes of the liver, among which the numerous branches of the Malpighian vessels are seen ; these 

 combine to form a pair of ducts which open into the dilated rectum. The organs of circulation 

 consists of a chambered heart or dorsal vessel situated in the abdomen, from which heart numerous 

 arteries are given off, while it is continued forward as an aorta into the cephalothorax. This divides 



LYCO.SA ANURENIVORA. 



A, under surface of female : on, falces ot 



chelicerse ; p, maxiliary palpus ; e, coxae ; 



st, stigmata: tp, >pinnerets. B, maxillary 

 palpus of male, much enlarged. 



