SENSES OF ARACHNIDA. 129 



touch, and darts out of its den upon the luckless captive. 

 Thus we frequently find the spider deeply seated in the 

 aperture of a wall, and the web extended to a considerable 

 distance over its surface ; and yet by the tension of the cords 

 composing the net-work, the spider is instantly made aware 

 of what occurs on every part of its surface. Two instances 

 are adduced in the work in question in support of the idea 

 that the eyes, and not the legs, are the instruments of know- 

 ledge"! to the spider. First, the long-bodied spider (Tetra- 

 gnatha extensa) is noticed as having probably given rise to 

 the popular opinion under review, notwithstanding it huddles 

 its legs into a close bundle, and which is evidently done 

 with the view of making them appear motionless, although 

 the insect does not the'less obtain information by their as- 

 sistance ; and immediately afterwards the long-legged house- 

 spider (Pholcus phalangioides) is referred to, as giving more 

 countenance to the opinion, because it keeps its legs spread 

 out as if to feel the more readily when any thing is caught, 

 although the more than usual prominence of its eyes is men- 

 tioned, as showing the superiority of its powers of sight. 

 I have noticed these contradictions, because, as they occur 

 in a work of great popularity, it is advisable that the errone- 

 ous impressions which they must necessarily produce should 

 be counteracted as early as possible. 



In the majority of the Arachnida, a complete and very dis- 

 tinct system of circulation exists. The heart is contained in 

 the abdomen, and in many species of spiders its pulsations 

 are easily to be observed. It consists of a large longitudinal 

 vessel, which emits a certain number of arteries, and receives 

 the veins by means of which the sanguineous fluid returns, 

 after having been aerated by the respiratory organs, to be 

 again distributed through the different parts of the body. 



In this class, as in the insects, the sexes are constantly 

 distinct, and impregnation is necessary for the fecundation 

 of the eggs. Several striking peculiarities are connected 



