ANATOMY OF THE SPIDER. 



359 



spW 1 



Fig. 311. Anatomy of a spider, diagrammatic longitudinal 

 section through the body, an, simple eyes and nerves leading 

 to them from the brain (supra-cesophageal ganglion, oG) ; 

 an y , mandibles ; fa 2 , palpus of maxilla J, ; / 2 . flrst P air of legs, 

 6, ~& 3 , succeeding pairs ; K, head ; Br, thorax ; /?, hind-body 

 or abdomen; ft if, heart or dorsal vessel ; L, lung in front of 

 the opening of the oviduct G ; the spinning-glands (sp) con- 

 nect with the spinnerets, sp W. The digestive tract is shaded, 



The type of the sub-class is the spider, which is character- 

 ized by the pos- 

 session of two 

 or three pairs 

 of spinnerets, 

 which are 

 jointed a p - 

 pendages ho- 

 mologous with 

 the legs. Be- 

 sides tracheae, 

 spiders have a 

 so-called lung 

 (Fig. 311, L), 

 composed of 



fj*~i/3j om^ccu.iii^ j/ana , JL\.^ nt'an , -ur ? LII\JIO,A. , L~M.^ iiiiiu.-uuu^ 



or abdomen; ft if, heart or dorsal ^essel ; L, lung in front of several leaVCS, 



into which the 



and in the abdomen enveloped in the liver. After Graber. -, -, 1 fl 



and is thus aerated. In Lycosa the blood flows through the 



heart from the head backward. There is a great range of 



structure, from the lowest 



mites to the spiders, certain 



mites having no heart, no 



tracheae, very rudimentary 



mouth-parts, and no brain, 



there being but a single 



ganglion in the abdomen. 



Order 1. Acarina. The 

 mites are the simplest 

 Arachnida, the body being 

 oval in form, the head 

 usually small, more or less 

 merged with the thorax, 



While the latter is not dif- Fig ^_ Ixod8 ampictm from a partly 

 fprpirHarpfl frrvm thp ahflo domesticated moose. The tick natural size, 



gorged with blood, and its six-legged young, 



men. There is a Slight much enlarged, o, beak or mandibles armed 



& . with teeth ; 6, maxilla, and c, maxillary pal- 



metamorphoSlS, the mite pus ; d, a foot with eucker and claws, en- 



when first hatched having arged ' 



but three pairs of legs, the fourth (and last) pair being added 



