RESPIRATION IN AIR 



57 



addition a pair of "tracheae." From a physiological point of 

 view these tracheae are analogous to the lungs. They do not 

 supply the tissues directly, 

 but serve mainly to aerate 

 the blood in the ventral sinus. 

 Lamy (1902) gives good fig- 

 ures from which the actual 

 dimensions can be obtained 

 for a considerable num- 

 ber of spider species. The 

 "tracheae" of Heliophanes cu- 

 preus which are unusually 

 large and richly branched 

 are shown in Fig. 33. Cer- 

 tain movements of the walls 

 of the lungs have been de- 

 scribed (Fraenkel, 1930) in 

 several forms. It is very 

 doubtful whether these bring 

 about any ventilation, but 

 certain that such ventilation, 

 if it exists, is of no conse- 

 quence compared with the diffusion which from the dimensions 

 must be ample. Zoond (1931) confirmed this and demon- 



Fig. 31. Book lung of spider. Dia- 

 gram. The length of the lung (v-tr) is 

 about 1.5 mm in Epeira diadema. (Mac- 

 Leod.) 



Fig. 32. Longitudinal section through scorpion showing lungs with spiracles, 



St. (Newport.) 



