Chap. III.] 



ARACHNIDA 



73 





duties. Respiration is effected by flattened processes 

 attached to the appendages behind the generative 

 pores (which are 

 always placed com- 

 paratively far for- 

 wards), and they 

 either carry blood 

 or contain air, or 

 disappear and are 

 replaced by tracheae. 

 The hinder part of 

 the body never 

 carries jointed ap- 

 pendages. 



1. Haemato- 

 br a ii chi at a. 

 These are to-day 

 represented by the 

 king-crab (Limulus ; 

 Fig. 30). In them 

 the respiratory la- 

 mellae contain blood, 

 and the hinder por- 

 tion of the body is 

 fused into a single 



O 



mass, while the ter- 

 minal spine is of 

 great length. 



2. IE rob raii- 

 cliia t a Such are 

 the scorpion (Scor- 

 pio ; Fig. 31) and the 

 spiders (Mygale). In 

 these the respiratory 

 lamellae are sunk into 



depressions of the body, and contain air (the so-called 

 lungs or lung-books). The hinder portion of the 



Fig. 33. Pentastomum tcenioides. 



A, Female, nat. size; B. male, nat. size; o, 

 head of male, enlarged. 



