The Arthropoda 



315 



to the maxillae (really attached to the thorax) are so modified that they, 

 too, belong to the mouth formation. The two pair of maxillae' and the 

 three pair of maxillipeds, together with the mandible, thus make six 

 pairs of jaws altogether. 



Back of these six pairs of jaws, a pair of pincers is attached to the 

 thorax proper. These are known as chelipeds ( ), 



and behind the chelipeds are four pair of walking legs. By observing 

 these legs it will be noticed that they are very much akin to the cheale 

 proper in that each has a broad attachment where it meets the body, the 



A. Mandible. B. First maxilla. C. Second maxilla. 

 bs. Basipodite. ex. Coxopodite. en. Endopodite. ep. Epipodite. 

 ex. Exopodite. sc. Scaphognathite. 



D. and E. First and second Maxillipedes. br. Branchial 

 filaments. cp. Carpopodite. dp. Dactylopodite. is. Ischiopodite. 

 me. Meropodite. prp. Propodite portions of endopodite. 



F. Third Maxillipede. cs. Coxopodite setae. 



G. Gill (—epipodite.) (After Latter.) 



protopodite ( ), composed of two portions, a coxopodite 



( ) and a basipodite ( ) which 



then join the pincer proper. These pincers consist of a solid immovable 

 portion, the exopodite ( ) and a smaller movable and 



inner portion, the endopodite ( ). 



It will be observed that the pincers are only enlarged walking legs. 



The portion of the crayfish directly behind the cephalothorax, with 

 the definite segmentation, is known as the abdomen and consists of six 

 segments, beside the tail. The tail consists of a central portion 

 called the telson ( ), and two pairs of leaf -like 



structures on each side called uropods, which assist in forming a broad 

 wing-like tail and which, when the crayfish is frightened, can be bent 



