236 ANNULATA. 



ducts of a large digestive gland and then is continued 

 as the rectum into the cloacal. sac. The spider kills 

 its prey by its poison chelicerae, bites it open with the 

 cutting bases of the pedipalpi, and sucks its juices by 

 means of its sucking stomach. The juices are stored in 

 the stomach and its caeca and digested and absorbed in 

 the intestine. We may note the absence of any crushing 

 gastric mill, so characteristic of the lobster and cockroach. 

 Again, we can observe a certain resemblance in the ali- 

 mentary system of the spider to that of the leech, due to a 

 similar method of feeding. 



The muscular system is much broken up into limb 

 muscles and other special muscles, and it is 

 difficult to recognise much trace of the annelid 

 and protracheate arrangement. 



The coelom has much the same relationship as in the 

 Insecta — that is, it is inferred that the perivisceral part is 

 not represented. There is a pair of small and 

 degenerate coxal glands which in some young 

 spiders open by a duct at the bases of the legs. These 

 are held to be vestigial excretory organs of the nephridial 

 type, and in the young scorpion they are said to have 

 internal openings into the coelom. 



The heart is a long dorsal tube surrounded by a peri- 

 cardial sinus into which it opens by three pairs of ostia. 

 The heart is continued forward into main arteries which 

 finally open into the venous sinuses composing the body- 

 cavity. Some of these communicate with the pulmonary 

 sacs and thence pass to the heart. The pulmonary sacs are 

 therefore in the same position in the blood circuit as are 

 the gills of the lobster and similarly the heart is systemic. 



The nervous system is concentrated in the cephalo- 

 thorax. It consists of a brain above the pharynx, supplying 

 the eyes and the chelicerae, and connected by a nerve-ring 

 .- with a ventral nerve-mass formed of at least 



five pairs of fused ganglia. From it nerves are 

 given off" to the pedipalpi, the legs and the abdominal 

 organs. Epeira shows a great degree of nerve-concentra- 

 tion and in this respect differs from some Arachnida. 



The vestigial excretory organs, or coxal glands, have 

 already been alluded to. The functional organs are four 



