G THE NATURAL HISTORY OF THE COMMON CRAYFISH. 



general hue may be red or blue. These are " cray- 

 fishes," and they oannot possibly be mistaken for any 

 other inhabitants of our fresh waters. 



XV 



FIG. 1. Astacus fluviatilis, Side view of a male specimen (nat. size) : 

 bff, branchiostegite ; eg, cervical groove ; r, rostrum ; f, telson. 

 1, eye-stalk ; 2, antennule ; 3, antenna ; 9, external maxillipede ; 

 10, forceps; 14, last ambulatory leg; 17, third abdominal ap- 

 pendage ; 20, lateral lobe of the tail-fin, or sixth abdominal 

 appendage ; xv, the first ; and xx, the last abdominal somite. 

 In this and in succeeding figures the numbers of the somites are 

 given in Roman, those of the appendages in ordinary numerals. 



The animals may be seen walking along the bottom 

 of the shallow waters which they prefer, by means of four 

 pairs of jointed legs (fig. 1); but, if alarmed, they swim 



