444 



COMPARATIVE ANATOMY 



CHAP. 



Pauropoda have the smaller number of 10 trunk segments (including 

 the anal segment). In the Chilopoda (Fig. 323, p. 464) and Biplopoda 

 the number of trunk segments is larger and often very considerable (in 

 Himantarhnn there are as many as 173). It is possible that this large 

 number of segments is not an original peculiarity of the Chilopoda and 



Pio. 301.— Soolopendrella immaoulata 

 (after Latzel). 



Fig. 302.— Campodea staphylinus, without 

 the setffi and hairs (after Lubbock). 



Diplopoda, but secondarily acquired, as in the serpents. In the 

 Diplopoda only the 4 or 5 anterior trunk rings represent single 

 segments, each subsequent ring is a double segment. 



Hexapoda. 



The body of the Hexapoda falls typically into 3 parts quite distinct 

 from each other : head, thorax, and hind body (abdomen). The un- 

 segmented head probably originally consisted of 4 segments. The 

 thopax is composed of 3 segments : prothopax, mesothorax, and 

 metathopax, answering to the 3 anterior trunk segments of the 

 Myriapoda. The typical number of segments of the hind-body is 10 or 

 11. The thorax and the abdomen together form the trunk, -which 

 may be compared with the trunk of the Symphyla. Among the 



