3° A SYNOPSIS OF ANIMAL CLASSIFICATION. 



the latter modification equipped 

 with a poison gland. 



X Vespa, Formica. 



Class III. ARACHIf OIDEA Head and thorax fused into a 



single piece, the cephalo-thorax, 

 bearing six pairs of appendages, of 

 which one is prae-oral. These 

 may all be used as legs, or one or 

 more pieces may be chelate and 

 serve as mandibles or weapons of 

 defence. In the lower forms the 

 abdomen is elongated and seg- 

 mented and may bear appendages, 

 but in the higher forms it is con- 

 solidated and may even be fused 

 with the cephalo-thorax. Respi- 

 ratory organs originally lamellate 

 gills, developed as adjuncts of the 

 abdominal appendages. In the air- 

 breathing forms they may be modi- 

 fied and reduced in number, or even 

 replaced by a tracheal system, 

 probably not homologous with 

 that of insects. 

 Sub-class I. ARACHHOIDEA Beamchiata .. Mainly fossil forms, all ma- 

 rine, gills lamellate, one pair of eyes 

 in side of cephalo-thorax, and one 

 pair of small ones anterior to these 

 near the middle line. Coxal joints 

 of the legs, or of some of them, 

 forming spiny plates used in mas- 

 tication. 



Order i, Gigantostraka Fossil crab-like animals with long 



extended abdomen, which may or 

 may not terminate in a spine. 



X Eurypterus, Pterygotus. 

 Order 2. Limuloidea Mainly fossil, with three surviving 



