MARINE AETHEOPODS 



273 



strong mandibles or jaws that move horizontally, and the two pairs 

 of maxilloB that are also employed in reducing the food. 



Following these, but belonging to the thorax, are three pairs 

 of appendages that are known as foot-jaws ; for, although they 

 assist the preceding organs in breaking up the food, they bear a 

 resemblance in some respects to the longer limbs behind them. Of 

 the latter there are five pairs (hence the term decapoda), the first 

 being a very powerful pair of seizers or pincers, and the remaining 

 four, which are well adapted for walking, terminating in either 

 double or single claws. 



All the appendages above 

 mentioned are not only attached 

 to the body by movable joints, 

 but are themselves made up of 

 jointed parts, sometimes a con- 

 siderable number, each of which, 

 like the segments of the body 

 itself, is surrounded by a ring 

 of hardened skin, and connected 

 with those above and below it 

 by a portion of soft and flexible 

 skin 



Lastly, beneath the abdo- 

 men, are paired limbs called 

 8'ivimmerets, which are used as 

 paddles, and probably assist 

 the animal more or less in its 

 progress through the water; but 

 the principal organ of locomotion 

 in the macrura is undoubtedly 



the powerful muscular abdomen, aided by the broad and fanlike tail 

 formed by the appendages of the last segment. To demonstrate this 

 fact, put a live lobster, or even a shrimp, in a still rock pool, and 

 threaten it from before, when it will rapidly retreat backwards by a 

 series of powerful jerks, produced by suddenly doubling its abdomen 

 forwards beneath its body. 



In addition to the external characters above mentioned, there 

 are many interesting features connected with the internal structure 

 of the lobster that may be studied on making easy dissections. 

 Thus, the gills, which are attached to the bases of the thoracic limbs, 

 may be exposed by cutting away the side of the carapace, and at tb.3 



T 



FIG. 205. APPENDAGES OF A 

 LOBSTER 



1. Second maxilla. 2. Third foot-jaw. 3. 

 Third walking leg. 4. Filch walking 

 leg 



