140 INVEItTKintATE ANIMALS. 



as ill the ce|ihalothorax, but are movably jniuteil together. The 

 variijiis appeiichiges oi the animal are arranged in pairs on the under 

 .surface of the body ; and wliere the segments are completely amal- 

 gamated (as ill the cephalothorax), their existence may nevertheless 

 be deterniiiied l)y the ]iresence of the successive pairs of appendages. 

 The first segment of tlie head carries a jiair of compound eyes, made 

 up of a-numljcr of simple lenses aggregated together, and supported 

 u])Ou long and movable eye-stalks. Beliind these come two pairs of 

 jointed organs of touch, whicli are known as the "antennce." The 

 front pair is much smaller than tlie hinder pair, and they are known 

 res]iectively as the "lesser anteniue," or "antennules" (fig. 87, a), 

 and the "great antenn.e" (f). Behind these, again, comes the 

 moutli, which is placed on the under surf.ice of the head, and is 

 provided with a complicated series of masticatory org;uis. It is 

 unnecessary to describe these minutely, but it should be noticed 

 that they are all modified limbs, and therefore differ altogether 

 from the jaws of tlie Vertebrate animals. That this is their real 

 nature is shown most oliviously in the hindermost pairs of these 

 jaws, whicli ale so little altered from ordinary legs that they are 

 known as "foot-jaws" (tig. 88, /). The last five segments of the 

 thora.x carry h\'e pairs of walking-legs, hence the name Decapoda 

 ajiplied to the order. (Jf these legs, tlie fir.st three jiairs have 

 their extreinitii's converted into nipiiing-claws or " cheUe," and the 

 first pair is iiiiich larger th.-iu the others, and constitutes the well- 

 known great ciaws of the Lobster. The last two pjairs of legs simply 

 terminate in jiointed extremities, and not in jiincers. The segments 

 of the aliilomeii, witli the exception of the fir.st and the hindmost, 

 carry each a pair of ]>addle-like ap]iendages, which are used in swim- 

 ming, and are called the " swimmerets." The last pair of swini- 

 nierets are attached to the last .segment but one, and are very 

 greatly expanded, so as to form ,a very powerful tail-fin (fig. 87, i). 

 The Last segment of ;dl is kiKiwn as the " telson " (y), and is not 

 ]H'0\'ided witli a,liy latel'al ;ip|)elldag(.'S. 



Tiie mouth ill the Lobster leads by a short gullet into a globular 

 stom.-ich, wliich is furnished Ayith .a ca.lcareous ajiparatus for grind- 

 ing down the fo(,d, coiiiiiionlv called the " laily in the lolister." The 

 intestine is continued backw.Lids from the stoniaeli \yithout convolu- 

 tions, and opens liy a distinct anus pl.-i,ced in front of the telson. A 

 wcll-develo|ied liyer is :ilso present. Tlie heart is ]il.-iced dorsafly, 



and is tilled with aerated bl 1 di'ri\-ed from the gills, which it pro- 



[lels tlirongh e\-ery part of the boily. Tlie gills, or branchiie, are 

 I'Viaiiiiilal bodies attached tii the bases of the legs, and )ilaoed in a 

 I-,mmI of ell,!, 111,,. r f,, lined beneath the great shield, or carapace, on 

 each sele of the boily. TIley consist each of a central stem support- 



