ARANEIDA 



531 



arterioles, but the blood is finally collected into sinuses which feed 

 the lung books when these are present. 



The nervous system is more concentrated than in the scorpion, 

 consisting of a supraoesophageal ganglion supplying the eyes (Fig. 363 ) 

 and a suboesophageal complex supplying the rest of the body. Two 

 non-ganglionated nerves pass backwards to the opisthosoma. 



The diagram (Fig. 361) shows a lung book opening in the anterior 

 part of the opisthosoma and the details of the structure are exhibited 

 in Fig. 355. The "leaves" of the book are seen to be thin plates with 

 an internal space for the circulation of the blood. They are dotted 

 with short chitinous spines (not seen) and fused with the walls of the 

 lung. The cavity of the lung only communicates by a narrow opening 



d.dig. Pf"^' h. 



Fig. 361. Diagram of a spider, Epeira diademata, showing the arrangement 

 of the internal organs, x about 8. From Warburton. an. anus; ar. artery; 

 brn. brain ; chc. chelicera ; cm. caecum of mid gut in ambulatory limb ; d.dig. 

 ducts of digestive gland ; e. eye ; ga.sb. suboesophageal ganglion ; gl.ac, gl.ag., 

 gl.am., gl.t. aciniform, aggregate, ampulliform and tubuliform glands ; h. heart 

 with three ostia ; Ing. lung book ; M. mouth ; m.d. dorsal muscle of sucking 

 stomach; 7ng. mid gut; m.t. Malpighian tubule; o. ov.ary ; p.gl. poison gland; 

 pcm. pericardium ; sp. spinneret ; s.p. stercoral pocket of hind gut ; s.st. sucking 

 stomach; v. vessel bringing blood from lung book to pericardium. 



with the outside air. Respiratory movements for the renewal of the 

 pulmonary air have not been recorded by most observers and the 

 method of respiration cannot be very efficient. In this diagram (Fig. 

 361) the tracheae are not shown, but in Fig. 355 A a horizontal section 

 through the opisthosoma is shown in which the same ingrowth has 

 given rise to a lung book and a bundle of tracheae. The character of 

 the tracheae is well seen. They spriAg from a long pocket in parallel 

 series and do not branch as in the insects, but they have the typical 

 structure, strengthened by a spiral ridge of the chitinous lining. This 

 form [Argyroneta) shows a richly developed tracheal system, but in 

 other forms, particularly spiders with slow movements, the number 



