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- 

 branctiiata. 

 These are to-day 

 represented by the 

 king-crab (Limulus ; 

 Fig. 30). In them 

 the respiratory la- 

 mellse contain blood, 

 and the hinder por- 

 tion of the body is 

 fused into a single 

 mass, while the ter- 

 minal spine is of 

 great length. 



2. jErobran- 

 ctiiata. Such are 

 the scorpion (Scor- 

 pio ; Fig. 31) and the 

 spiders (Mygale). In 



flipop fhp rpcnriratrvrv A Female, nat. size; B. male, nat. size ; o, 



inese T-ne respiratory head ()f lualei en i arg ed. 



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. 



