38 OUTLINES OF NATURAL HISTORY. 



As regards the internal anatomy of the Spider, little 

 need be said. The digestive system presents no remark- 

 able peculiarity, except that the throat is extremely nar- 

 row; a -wide throat not being necessary for an animal 

 ■which lives merely upon the juices of its prey. The intes- 

 tine terminates in a distinct vent, and there is a well-devel- 

 oped liver. The heart has the form of a long tube placed 

 along the back; and the nervous system has, in the young, 

 the form of a chain of nervous masses placed along the 

 lower surface of the body. In the adult, however, these 

 masses are aggregated and amalgamated -svith one another, 



Tegenaria civilis attains a length of nearly half an inch, 

 and is the common House Spider of Britain. It spins a 

 horizontal web, appended to which is a short open tube, 

 into which the animal retreats when threatened with dan- 

 ger, and from which it watches for insects which may fall 

 into its snare. It is mostly of a reddish-brown colour, 

 with black markings. It lays its eggs in little packets of 

 fifty or sixty each, all kept together by delicate silken 

 fibres. Several of these packets are constructed and are 

 attached to walls or other objects in the neighbourhood of 

 the web. The young Spider is like its parent, but is much 

 smaller ; and it changes its skin no less than nine times 

 before it assumes the characters of the adult. Its entire 

 span of life appears to extend over four years. 



Recapitulation of Essential Characters. — The 

 body is composed of a series of rings placed one behind 

 the other ; and those rings which belong to the head and 

 trunk (thorax) are amalgamated together. There are four 

 pairs of legs. The abdomen never carries legs. The 

 animal breathes air directly. The heart (if present) is 

 situated on the back, and the nervous system has, at any 

 rate to begin with, the form of a chain of little nervous 

 masses placed along the lower surface of the body. The 

 feelers ("antennre") which are so characteristic of Insects, 

 when present at all, are converted into oflfensive weapons 

 (poison -fangs or pincers). These characters distinguish 

 the Arachnicla as a whole. 



