40 



ORGANS OF SUPPORT. 



FIG. 18. 



arched plate, or carapace, and supports the usual appen- 

 dices for mastication, sensation, and locomotion. There 

 are two strong mandibles, with their palpi attached to 

 them, at the sides of the mouth ; two pairs of slender 

 maxilke, also provided with palpi ; and exterior to these 

 there are three pairs of larger convertible maxillae, or feet- 

 jaws, with their attached jointed palpi, as seen in the 

 larger decapods, as in the astacus fluviatilis, represented in 

 Fig. 18. There are two pairs of antennae, the inner pair 

 (, a,) of which are commonly divided at their free ex- 

 tremities, and the exterior larger pair (b, b,) have at their 

 proximal extremity, in their 

 broad expanded basilar joint, 

 the small circular prominent 

 opening of the vestibule or 

 ear, on each side, directed 

 downwards, sometimes co- 

 vered with a membrane, and 

 sometimes with a calcined 

 plate. The eyes (c, c,) are 

 compound, generally pedun- 

 culated and moveable, some- 

 times fixed or sessile. The 

 upper and anterior part of the 

 cephalo-thorax is occupied by 

 the stomach ( e, ) with its 

 strong muscular and osseous 

 apparatus, and containing 

 five teeth. In the middle of 

 the posterior part of the ce- 

 phalothorax is seen the pro- 

 jecting portion which covers 

 the heart (/). Towards the 

 sides are seen the two curved longitudinal lines on the 

 carapace, which mark the internal attachment of the mem- 

 branous diaphragm, which separates the respiratory cavities 

 on the sides from the abdominal viscera contained in the 

 middle portion of the cephalothorax. The anchylosed 

 segments of the cephalothorax send inwards and upwards 

 numerous vertical thin calcified plates, which give attach- 

 ment to the muscles of the haunches, and by meeting 



