140 INVERTEBRATE ANIMALS. 



as in the cephalothorax, but are movably jointed together. The 

 various appendages of the animal are arranged in pairs on the under 

 surface of the body ; and where the segments are completely amal- 

 gamated (as in the ceplialothorax), their existence may nevertheless 

 be determined by the presence of the successive jjairs of appendages. 

 The first segment of the head carries a pair of compoimd eyes, made 

 up of a number of simple lenses aggregated together, and supported 

 upon long and movable eye-stalks. Behind these come two pairs of 

 jointed organs of touch, which are known as the " antennae." The 

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

 respectively as the " lesser autennte,'' or " antennules " (fig. 87, a), 

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

 mouth, which is placed on the under surface of the head, and is 

 provided with a, complicated series of masticatory organs. It is 

 unnecessary to describe these minutely, but it should be noticed 

 that they are all modified limbs, and therefore diff'er altogether 

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

 nature is shown most obviously in the hindermost pairs of these 

 jaws, which are so little altered from ordinary legs that they are 

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

 thorax carry five pairs of walking-legs, hence the name Decapoda 

 applied to the order. Of these legs, the first three pairs have 

 their extremities converted into nipping-claws or " cheke," and the 

 first pair is much larger than the others, and constitutes the well- 

 known great claws of the Lobster. The last two pairs of legs simply 

 terminate in pointed extremities, and not in pincers. The segments 

 of the abdomen, with the exception of the first and the hindmost, 

 carry each a pair of paddle-like appendages, wliich are used in swim- 

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

 merets 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 all is known as the " telson " (J), and is not 

 provided with any lateral appendages. 



The mouth in the Lobster leads by a short gullet into a globular 

 stomach, which is furnished with a, calcareous apparaUis for grind- 

 ing down the food, commonly called the " lady in the lobster." The 

 intestine is continued backwards from the stomach without convolu- 

 tions, and opens by a distinct anus placed in front of the telson. A 

 well-developed liver is also present. The heart is placed dorsally, 

 and is filled with aerated blood derived from the gills, which it pro- 

 pels through every jjart of the body. The gills, or branchiie, are 

 pyramidal bodies attached to the bases of the legs, and placed in a 

 kind of chamber formed beneath the great shield, or carapace, on 

 each side of the body. They consist each of a central stem support- 



