WOOD-LICE AND WHALE-LICE. 



535 



always seven pairs of legs, and the abdomen and its appendages are 

 also well developed in some families, tlio hinder segments bearing long 

 legs adapted for leaping. This description applies 

 best to the Oammaridce, one or two of which, that 

 live in fresh water, grow to the length of half an 

 inch. The greater part of the AmpMpoda, however, 

 are marine, and differ considerably in size, shape, and 

 habits. Some swim freely in the water, and others burrow 

 into woodwork. Many are in the habit of attaching them- 

 selves to various marine animals ; and one family, Lmnodi- 

 podidw, in which the abdomen is rudimentary, is truly 

 parasitic. One curious genus, Cyamus (Lamarck), which is 

 parasitic on whales, has strong hooked appendages at 

 both ends of the body; and the species are known as Whale- 

 Lice. We have figured 0. ovalis (Roussel). 



Fig. 9.— 

 \Vhale-Louse 

 (Cyamus ovalis). 



Nat, gize. 



Order II. — Thoracostraca. 



The present order agrees with the last in the number of segments, but is 

 distinguished from it by having more or fewer of the thoracic segments 

 united with the head by a common shell, or carapace, and there are usually 

 two compound stalked eyes. We find no true parasites in this group, though 

 some of them seek the society of other animals for the sake of food and 

 shelter, as in the case of the small crab which takes up its residence in the 

 shell of the Pinna. 



Sub-Order I. — Cumacea. 



Includes small marine species, with sessile eyes, and a long, slender 

 abdomen. 



Sub-Order II. — Stomatopoda. 



This order is now restricted to the single (amilj S;£HilUdce, which are marine 

 Crustacea resembling large prawns, three inches or more in length, with the 



cephalothorax slender, a 

 large tail-fin, and the 

 second pair of foot-jaws 

 developed into an enor- 

 mous claw, which has 

 led to one of the com- 

 mon species being called 

 Squilla mantis (Eondel), 

 on account of the shape 

 and attitude of its legs 

 very closely resembling 

 the predaceous legs of 

 the Mantidie among the 

 Orthoptera. This species 

 swims strongly, and is 

 eaten in Italy, where it 

 attains a length of six inches ; in the British seas it does not exceed ^ 

 inches in length. 



Fig. 10. — Squii,i.a mantis, 

 ^ Nat. size. 



