SECT. vii. DECAPOD CRUSTACEA. 191 



structed that the crab can bend the eye-stems horizon- 

 tally to the right and left, and the front of the carapace 

 either conceals the orbit, or forms the eyebrow. 



In all crabs the antennae appear in front between the 

 eyes. The first or interior pair are short, jointed, and 

 capable of being bent into cavities, which contain their 

 basal joints ; these cavities are near the eye orbits, with 

 which they are connected in cer- 

 tain species. Well-developed ears 

 are placed in their basal joints. 

 Fig. 146 represents a magnified 

 ear seen from behind, and Mr. 

 Gosse mentions that the large 

 eatable crab, whether at rest or 

 feeding, carries these antennae 



T , , j i j.i_ Fig. 146. Ear of Crab. 



erect and elevated, always on the 



watch, and either vibrating them, or incessantly striking 



the water with them in a peculiar jerking manner. 



The exterior or lower pair of antennae are always 

 longer than the interior pair ; sometimes they are simple 

 and similar to them, as in the flat crabs ; and sometimes 

 they have jointed filaments at their extremities. In all > 

 the species they are attached to the under-side of the 

 crab, and the organs of smell are openings at the point 

 of junction between their second and third joints. 

 These openings, which lead into the mouth, are covered 

 by a membrane, and closed by a calcareous lid. Each 

 lid is fastened by a little hinge to the side of its cavity, 

 and is opened and shut by muscles fixed at the ex- 

 tremity of a long tendon. Thus the lower antennae are 

 the organs of smell, while the upper pair are the organs 

 of hearing, and both are probably the organs of touch. 



The mouth of the crab is on the under part of the 

 head, its lips are horny plates, and it has a pair of 

 mandibles to cut the food ; their action is from side to 

 side. On each side of the mouth there are two pairs of 



