4 BRITISH BEETLES. 



The members of the next class, Arachmda, have mostly 

 eight legs, though some have ten ; their body is com- 

 posed of two distinct parts, the head (or cephalo -thorax] 

 and abdomen, in some cases even these being joined so 

 closely as scarcely to admit of distinction. In others^ 

 the Scorpions, etc., the abdomen is composed of many 

 rings, and the palpi are developed so as to look like two 

 additional legs. They are all without antennae, and 

 wingless, arid do not undergo the complete metamor- 

 phoses of insects, being mostly hatched at once from the 

 egg, and growing afterwards only in size ; they breathe 

 either through internal air-gills (pulmonary sacs), or by 

 radiated tracheae, varying from two to eight in number, 

 and opening into spiracles (or breath-holes) on the lower 

 part of the abdomen or sides of the head ; their covering 

 is mostly leathery (but harder in the Scorpions), and 

 their eyes vary from two to eight, being placed in dif- 

 ferent positions on the head (or cephalo -thorax] ; the 

 heart is long and large, circulation taking place by 

 means of arteries and veins, and the sexes are always 

 distinct, as in insects ; they mostly possess the peculiar 

 faculty of reproducing their limbs when mutilated, and 

 they engender more than once during life, both which 

 circumstances assist in separating them from the latter 

 class. Spiders, Scorpions, and Mites are well-known 

 representatives of the Arachmda. 



The Insecta, by far the most numerous in species of 

 any corresponding group throughout the animal king- 

 dom, have in their perfect state six legs only (although 

 in these, as in other organs, some are often abnormal or 

 undeveloped), two antennae, and two compound eyes, 

 composed of many facets. They differ from the Crus- 

 tacea in always breathing atmospheric air through late- 



