ARACHNIDA. 203 



the haunches, and the succeeding ones the leg, and the tarsus, 

 and each foot is terminated by two, or sometimes three hooks. 

 Besides these, there are other members, resembling feet, 

 which are placed in front of the head, and have affixed to 

 them either a moveable hook, or pincers, which are employed 

 as organs of prehension, and of offence. Through the larger 

 branches of these a canal passes, which opens near the point, 

 and conducts a poisonous fluid into the wounds inflicted by 

 this formidable weapon. 



In common with all articulated animals, spiders, in the 

 progress of their growth, cast off* their outer skin several 

 times, and at regular periods. In the earlier stages of their 

 existence, although they have the general form of the ma- 

 ture insect, yet they have a smaller number of legs: the last 

 pair not making their appearance till after the spider has at- 

 tained a certain size. We may here trace the commence- 

 ment of that system of metamorphosis, w^hich, as we shall af- 

 terwards find, is carried to so great a length in winged insects. 



Spiders are endowed with extensive powers of progres- 

 sive motion, and display great activity and energy in all 

 their movements. The long and elastic limbs on which the 

 body is suspended, being firmly braced by their articulations, 

 enable the muscles to act with great mechanical advantage 

 in accelerating the progression of the body. Hence, these 

 animals are enabled to run with great swiftness, and to 

 spring from a considerable distance on their pre}'; powers 

 which were necessary to those tribes that live altogether by 

 the chase. The greater number of species, however, as is 

 well known, are provided with a curious apparatus for 

 spinning threads, and for constructing webs to entangle flies 

 and other small insects. Every species of spider weaves 

 its web in a manner peculiar to itself: and, besides the prin- 

 cipal web, they often construct in the neighbourhood a 

 smaller one, in the form of a cell, in which they conceal 

 themselves, and lie in ambush for their prey. Between 

 this cell and the principal web they extend a thread of com- 

 munication, and by the vibrations into which this thread is 

 thrown, on the contact of any solid body, the spider is im- 



