432 



PHYLUM ARTHROPODA 



with three fused and three free segments, and an unsegmented rudi- 

 mentary abdomen. Four somewhat primitive eyes on an anterior 



hillock are nearer to the eyes 

 of Arachnoids than to those of 

 any other class. There are 

 typically seven pairs of append- 

 ages. The first are short and 

 chelate, but may be absent in 

 the adult. The next two are 

 small and slender, and are often 

 absent in the adult female ; the 

 second pair may also be absent 

 in the male, but the third in the 

 males of all genera carries the 

 eggs. The last four pairs of 

 appendages are always present, 

 and form the walking legs. Into 

 them, and into the cheliceraj 

 when these are present, out- 

 growths of the mid-gut extend. The sexes are separate. The larvse 

 are at first unsegmented, with three pairs of appendages. 



Fig. 245. — Sea-spider (Pycnogonum 

 litturale), from the dorsal surface. 



Fig. 246. — Male of Nymphon. — After Sars. 



PR., Proboscis ; CH., chelophores ; P., pedipalps ; £., eggs carried on 

 ovigerous legs ; A., rudimentary abdomen. 



Examples. — Pycnogonum, Nymphon, Ammothea. In Pentanymphon 

 and Decolopoda there is an extra pair of long walking legs. 



