ANNULOSA I CH^TOGNATHA. 2 I J 



length. The following are the characters ascribed to the class 

 by Huxley : 



" The head is provided with several, usually six, sets of 

 strong, bilaterally symmetrical oral setae, two of which, long 

 and claw-like, lie at the sides of the mouth ; while the other 

 four sets are short, and lie on that part of the snout which is 

 produced in front of the oral aperture. The posterior part of 

 the body is fringed on each side by a delicate striated fin-like 

 membrane, which seems to be an expansion of the cuticle. In 

 some species the body is beset with fine setae. The intestine is 

 a simple, straight tube, extending from the rnouth to the anus ; 

 the latter opens on the ventral surface, just in front of the 

 hinder extremity. A single oval ganglion lies in the abdomen, 

 and sends, forwards and backwards, two pairs of lateral cords. 

 The lateral cords unite in front of and above the mouth into 

 a hexagonal ganglion. This gives off two branches which 

 dilate at their extremities into the spheroidal ganglia, on which 

 the darkly pigmented imperfect eyes rest. The ovaries, 

 saccular organs, lie on each side of the intestine and open on 

 either side of the vent ; receptacula seminis are present. Behind 

 the anus, the cavity of the tapering caudal part of the body is 

 partitioned into two compartments ; on the lateral parietes of 

 these, cellular masses are developed which become detached, 

 and floating freely in the compartment, develop into "sperma- 

 tozoa. These escape by spout-like lateral ducts, the dilated 

 bases of which perform the part of vesiculce. seminales. The 

 embryos are not ciliated, and undergo no metamorphosis " 

 (See Introduction to the Classification of Animals, p. 52). 



CHAPTER XXX. 



ARTHROPODA. 



DIVISION II. ARTHROPODA, OR ARTICULATA. The remaining 

 members of the sub-kingdom Annulosa are distinguished by 

 the possession of jointed appendages, articulated to the body ; and 

 they form the second primary division often called by the 

 name Articulata. As this name, however, has been employed 

 in a wider sense than is understood by it here, it is, perhaps, 

 best to adopt the more modern term Arthropoda. 



The members of this division, comprising the Crustacea, 

 (Lobsters, Crabs, &c.), the Arachnida (Spiders and Scorpions), 



