104 DIVERSIONS OF A NATURALIST 



better, an edible crab, and a lobster, and a large prawn, 

 you will find that they all have five pairs of legs con- 

 verted into short foliaceous jaws (hence called " foot- 

 jaws"), and overlying the first very strong pair, or 

 mandibles. 



Following these " foot-jaws " you find in a crab 

 or a lobster the great nipping claws and the four large 

 walking legs — the same in proportion and shape in crab, 

 lobster, and prawn, much bigger than the foot -jaws. But 

 the curious thing is that if you set them out and carefully 

 compare them (for they are not simple jointed limbs, but 

 each has two or even three diverging stems carried on a 

 basal joint), you will find a strange and fascinating 

 " likeness in unlikeness," or an agreement of the parts of 

 which they are built, and yet a difference between all 

 of them. 



The rings of the body to which the jaw-legs and legs 

 are attached are fused into one unjointed piece. The 

 spine in front of the mouth and the support of the eyes 

 and the feelers or " antennae " are fused with that piece. 

 It forms on the back a great shield — often called " the 

 head " — which overhangs and is bent down over the sides 

 of this region, so as to protect the gills, which you can 

 see by cutting away the overhanging flap. 



Following on the jaw-legs or foot-jaws and walking- 

 legs, in the three crustaceans we are looking at, comes the 

 jointed tail or hind-body, consisting of seven pieces. 

 The first five rings of the tail have small Y-shaped 

 legs, a pair to each ring. They are called " swimmerets," 

 whilst the sixth has legs of the same shape, but very 

 large and flat. In the middle between these large flat 

 legs is the last ring, which has no legs, but is perforated 



