SPIDERS. 



105 



the oesophagus, and so into the stomach. At the end of the oesophagus is the sucking- 

 stomach. This consists of a flattened tube, to the top of which is attached a muscle 

 connected with the back; and to the bottom, other muscles attached to a tough 

 diaphragm spreading across the cephalothorax, and fastened between the legs on each 

 side. When these muscles contract the top and bottom of the sucking-stomach are 

 drawn apart, and whatever is in the oesophagus is sucked in. By this pumping motion 

 the spider takes liquid food from the mouth and drives it backward into the abdomen. 

 Just behind the sucking-stomach the intestine gives off two branches, which extend 

 forward around the stomach muscle and meet over the mouth. Each of these branches 

 gives off on the outer side four smaller branches which extend downward, one in 

 front of each leg, uniting on the under side of the thorax. The intestine con- 

 tinues backward through the abdomen to the little knob behind the spinnerets. The 

 brown mass which surrounds the intestine, and fills the abdomen above it, is the liver, 

 which discharges into the intestine at several points. 



FIG. 145. Section of Epeira vulc/aris, garden spider, a, b. Upper and lower lips. c. (Esophagus, d, f. Upper 

 and under muscles of the sucking-stomach, e. Stomach. J. Post-oral ganglion, k. Brain. /. Nerves to the legs 

 and palpi, in. Branches of the stomach, n. Poison-gland, o. Intestine, p. Heart. R. Pulmonary sac. S. Ovary. 

 t. Air-tube, u. Spinning-glands. 



Over the intestine and parallel with it is the heart, a muscular tube with open- 

 ings along the sides to receive the blood, and branches through which it flows to 

 different parts of the body. The greater part of the blood enters near the front of the 

 heart, and passes backward into the abdomen or forward into the thorax. In the front 

 of the abdomen are the principal breathing-organs, or lungs, a pair of sacs contain- 

 ing a number of thin plates, through which the blood passes on its way to the heart. 

 Besides these there is a pair of trachea opening near the spinnerets. 



The spinning-glands lie above the spinnerets, along the lower portion of the abdo- 

 men. They will be more fully described when we come to discuss the webs. The 

 reproductive organs lie along the under side of the abdomen, and open between the two 

 lungs. 



Persons unfamiliar with spiders find it hard to tell young from old, and male from 

 female. This is caused by the great differences between different ages and sexes of the 

 same spider. The adult males and females are, however, easily distinguished from 

 each other, and from the young, by the complete development of organs peculiar to 

 each sex, which will be described further on. The males are usually smaller than the 

 females, and have, in proportion to their size, smaller abdomens and longer legs. They 

 are usually darker colored, especially on the head and front parts of the body ; and 

 markings which are distinct in the female run together and become darker in the male. 



