THE CRAYFISH. 131 



cheal, sometimes pulmonary. The head and thorax, in- 

 stead of being separate, as in the two preceding groups, 

 are joined in a single piece, the cephalo- thorax. All 

 have four pair of limbs. Spiders and scorpions are arach- 

 nids. 



IV. The Myriapods are distinguished by bodies com- 

 posed of numerous rings, all alike after the head, and 

 each carrying one or two pair of legs. Consequently 

 the number of feet is quite large in all the myriapods, 

 and they are commonly called centipedes or thousand- 

 legs. 



CHAPTER XIV. 

 The Crayfish. 



THE crayfish is a crustacean. Crustaceans owe the 

 name to their hard carapace, stiffened with calcareous 

 matter. The color of the crayfish is variegated blue and 

 red. The head has projecting eyes, said to be pedicu- 

 lated or stalked, and two pair, of antennae of unequal 

 length. The mouth is situated in a sort of depression, 

 partly covered by the region of the antenna?, and sur- 

 rounded by six pair of articulated processes, which are 

 only so many limbs modified for the purposes of prehen- 

 sion and mastication of the food. 



The first pair one of which is at each side of the 

 mouth, and which are covered by the others constitute 

 the mandibles. The mandibles are short, thick, and pre- 

 sent a large surface and sharp edges ; they are specially 

 adapted for mastication, and each has a little lateral 

 process called the maxillary palp, or feeler of the jaw. 



