SENSES OF ARACHNIDA. 127 



thorax constitutes the abdomen ; in general it is soft, more 

 or less globular ; on its under surface are to be observed a 

 certain number of apertures or spiracles, and the anal aper- 

 ture, as well as the spinnerets, when present, are placed at 

 its posterior extremity. 



The external covering of the Arachnida may be regarded 

 as of a leathery, rather than a horny texture, but in some 

 species it assumes a considerable degree of rigidity ; it forms, 

 however, in all cases, an external skeleton, to which the 

 muscles are internally affixed, as in insects. 



Of the senses of the Arachnida, it may be observed that, 

 according to the best of our necessarily imperfect knowledge 

 of such matters, they appear to possess all the five senses 

 with which the higher animals are endowed : that the minute 

 simple stemmata on the crown of the metathorax are eyes, 

 and that these animals possess the sense of sight, cannot be 

 doubted ; everybody having observed the hunting spider 

 (Salticus) throw itself to a considerable distance upon its 

 prey. Here it is evident that the instinct of the animal, 

 acting upon the impressions produced by the possession of 

 the sense of sight, induces it to do an act for the gratifica- 

 tion of another sense that of taste. In like manner, the 

 sense of touch is possessed in an eminent degree by these 

 animals ; and although the accuracy of the poet's observa- 

 tion, that the spider 



" Lives in each thread, and feels along 1 the line," 



has been called in question in a very popular work (Insect 

 Miscellanies, p. 5), I am convinced, from experiments which I 

 have made for the express purpose of ascertaining the rela- 

 tive powers of the senses of sight and touch, that the latter 

 is much stronger than the former. When a fly is caught in 

 the web of a spider, the latter instantly stretches out its legs 

 in the direction of the captured and struggling insect, and 

 feels, for in no other manner can I describe its proceedings, 



