ARANEIDA 



459 



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. 339) 

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

 non-ganglionated nerves pass backwards to the opisthosoma. 



The diagram (Fig. 337) shows a lung book opening in the 

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

 exhibited in Fig. 330. 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 



d.dig. 



pcm. 



gl-ag- 



Pl.t. I sp. 

 ^ gl.ac. 



Fig. 337. Diagram of a spider, Epeira diademata, showing the arrangement 

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

 hrn. brain; chc. chelicera; C7n. caecum of stomach; 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; 

 mg. mid gut; m.t. Malpighian tubule; o. ovary; p. gl. poison gland; pcm. peri- 

 cardium ; sp. spinneret ;s.p. stercoral pocket of end gut is.st. sucking stomach ; 

 V. vessel bringing blood from lung book to pericardium. 



narrow opening 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. 337) the tracheae are not shown, but in Fig. 330 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 spring 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. 



