294 TEXTBOOK OF ZOOLOGY 



and the anterior portion of the stomach, which is called the sucking 

 stomach. The posterior portion of the stomach gives off five caeca 

 which are supplied with blood vessels from the anterior aorta. The 

 intestine passes through the small waist connection into the abdomen 

 and becomes enlarged in two portions, one for the reception of the 

 hepatic ducts from the liver and the other at the posterior end for 

 the formation of a stercoral sac or pocket. 



The excretory wastes are removed by the Malpighian tubules, which 

 discharge into the posterior portion of the intestines, and by vestigial 

 coxal glands. 



The vascular system consists of a muscular tube or heart, arteries, 

 and veins, located above the intestine. The heart receives its blood 

 from the body by means of three pairs of ostia. It is then forced 

 anteriorly through the aorta into the cephalothorax and also pos- 

 teriorly into the abdomen. 



The nervous system is composed of a large ganglion in the cephalo- 

 thorax which is connected with a dorsal brain by a nerve ring around 

 the esophagus. Nerves pass from the ganglion to the limbs and the 

 abdomen. 



The respiratory functions are carried on by the lung books or 

 sacs, which contain a number of thin plates through which the blood 

 passes on its way to the heart. In the posterior part of the abdomen 

 is a pair of branching air tubes or tracheae. This system of breathing 

 is found only in the arachnids. 



The reproductive organs consist of the ovaries in the female and 

 the testes in the male. The female has two sets of openings, one to 

 receive the sperms into the sacs, from the tips of the pedipalps, and 

 the other is the exterior opening of the oviducts. The male and fe- 

 male openings are near the lung books. The eggs are fertilized within 

 the body of the female and then laid in silken bags or cocoons. In 

 many species these egg bags are carried on the abdomen of the female. 

 The rate of growth of the eggs varies according to the conditions. 

 For example, eggs laid in the autumn develop slowly all winter, while 

 those laid in the summer develop within a few days. The hatching 

 takes but a day or two. The young spider is pale and soft bodied, 

 but in a few days it molts for the first time and then begins to look 

 like an adult spider. As the spider grows, it molts a number of times, 

 the development being direct. If the young spiders do not get out 

 of the cocoon soon enough, so that they have their freedom, they 



