110 INV^ERTEBRATE ZOOLOGY. 



83. Auatomical Si/no2isis. 



[A spider should be dissected in the same general way as other Arthropods ; the specimen 

 opened from the dorsal side by cutting around the eyes and removing the entire dorsal wall, 

 and then dissected under weak alcohol, pinned down in a small glass pan. As the specimens 

 should be large and fresh, it is impossible to proviae material for a large class. Students 

 finding good specimens may malie a general dissection, employing the following synopsis :] 



1. Alimentary canal. Muscular pharynx — long, narrow oesophagus, 

 running through a mass of nerve ganglia — thoracic enlargement 

 with paired diverticula reaching into legs and running around to the 

 ventral .side — an abdominal portion, also showing a few diverticula, 

 (This, together with the thoracic enlargement, forms the chyle- 

 stomach.) — the short rectum and large rectal vesicle, a sort of cloaca 

 — a pair of Malpighian or iirinary tubules which empty into the 

 rectiTm. 



3. Nervous system. An almost solid mass, perforated by the oesophagus 

 and giving out paired nerves to the ej'es, appendages, abdominal vis- 

 cera, etc. The portion dorsal to the oesophagus represents a supra- 

 oesophageal ganglion and the ventral portion, the consolidated ven- 

 tral chain. Some forms have a single small ventral ganglion just 

 posterior to the main mass. 



3. Circulatory system. A dorsal vessel or " heart " in the median line of 



the abdomen, with three pairs of ostia to receive the blood from the 

 body, and anterior, posterior and lateral aortae, to send it to the dif- 

 ferent parts. These arteries are short and with open ends, the re- 

 mainder of the circulation being lacunar. 



4. Respiratory system. Fan tracheae consisting of hanging plates with 



double walls. The blood passes down between the walls of each i^late 

 and is aerated by the supply of air in the respiratory chambers. Trach- 

 eal tubes somewhat similar to those of insects, a single median tube 

 arising from the single stigma, which branches into two main stems, 

 furnished with little tufts of tracheal tubes. 



5. Reproductive system. Male : Two long tubular testes in abdomen, 



becoming gradually more attenuated to form the vasa deferentia, 

 which are often much convoluted. They unite at the end and open 

 by a median orifice. The pedipalpi serve as copulatory organs. The 

 inner side of the terminal joint contains a spiral tube opening at the 

 apex. This is filled with spermatozoa, which are thus conveyed to 

 the recei)tacula of the female. Female: The two ovaries are tubu- 



