6 THE NATURAL HISTORY OF THE COMMON CRAYFISH. 
general hue may be red or blue. These are “ cray- 
fishes,” and they cannot possibly be mistaken for any 
other inhabitants of our fresh waters. 
y 
Fig. 1.—Astacus fluviatilis—Side view of a male specimen (nat. size) : — 
bg, branchiostegite ; cg, cervical groove; 7, rostrum ; ¢, 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 
