MARINE ARTHROPODS 269 



a clean skeleton. Although they are all small creatures, they 

 make up in numbers for any deficiency in size ; and though 

 devoured in enormous quantities by the various shore birds, they 

 multiply so prodigiously that they are never lacking wherever 

 there is decomposing organic matter to be consumed. 



The bodies of these animals are usually flattened from side 

 to side, very distinctly segmented, and have a well-developed 

 abdomen. The head is furnished with two pairs of antennae and 

 a pair of sessile eyes, though some species possess only one pair 

 of antennae, while others have four eyes. The limbs of the thorax 

 are used either for walking or for swimming, and give attachment 

 to the gills. The abdomen has generally six pairs of appendages, 

 the foremost three pairs of which are usually small, and employed 

 in swimming, while the others are stronger and directed back- 

 wards, and are often adapted for jumping. 



It is very interesting to observe the habits of the Sandhoppers 

 and other Amphipods both on the sandy beach and in the water, 

 and the student will find that certain species burrow into the sand 

 with considerable agility, and live principally at the extreme high- 

 water mark, where they feed on the organic matter washed in by 

 the breakers at each high tide, while others dwell almost exclu- 

 sively in the water, among weeds and stones, and should be 

 searched for at low water. The latter may be kept alive for some 

 time in the aquarium providing they are the only occupants, but 

 a little experience will show that these and all other Amphipods 

 are readily devoured by many marine creatures, and consequently 

 they are of real value to the aquarium keeper as food for other 

 animals. 



We now come to the Stalk-eyed Crustaceans (Podophthalmata), 

 which contain those members of the class most generally known, 

 such as crabs, lobsters, shrimps, and prawns. In these the eyes 

 are mounted on movable pedicels, the head and thorax are generally 

 covered by a large shield called the carapace, and the appendages 

 are adapted partly for seizing and masticating, and partly for 

 locomotion. 



The group includes two orders the Stomapoda or Mouth- 

 footed crustaceans, so called because some of the limbs are crowded 

 round the region of the mouth ; and the Decapoda, or Ten-footed 

 crustaceans. 



The Stomapods, though very abundant in tropical seas, are 

 not often met with on our own shores. However, since a few 



