Crabs, Lobsters, Shrimps, Barnacles, etc. (Crustacea). yg 



and on the under surface is the mouth, furnished with six pairs 

 of appendages or feet modified for purposes of mastication. Of these 

 first we have a pair of mandibles followed by two pairs of maxillae, 

 forming the "jaws" of the Lobster. Then there are three pairs 

 of "foot-jaws" or maxilhpedes, used by the animal to hold and 

 turn about his prey or food, while the jaws proper are employed 

 for biting and chewing. The working of this apparatus (in which 

 an upper jaw does not work against a lower as ours do when we 

 are chewing, but the jaw of one side grinds against that of the 

 other), can be very well seen while the animal is eating. Behind 

 the foot-jaws we find five pairs of walking-legs, the first three 

 pairs of which end in pinching claws. The claw of the first pair 

 of these walking-legs are of immense size and strength, and serve 

 as weapons of attack or defence. The tail also bairs a pair of 

 limbs on each joint; they are termed the swimming-legs, but serve 

 in the female Lobster to carry the eggs. 



If we observe the Lobster more carefully, it seems to be con- 

 stantly fanning itself with the feathery tassels on its foot-jaws, 

 and often performs similar movements with its abdominal legs. 

 This is its method of breathing. Just as man renews the air in 

 his lungs by the contraction and expansion of his chest, so the 

 Lobster, by these movements of its feet, causes fresh water to 

 flow to its gills, which lie under its shell at the base of the legs. 

 Another noticeable action is the constant twitching of the smaller 

 pair of feelers; these probably serve as olfactory organs, while 

 the larger ones are the organs of touch. 



An important event in the life of a crab or lobster is the period- 

 ical moult, more frequent in young than in older animals. For 

 the skin of the crustacean has not only the function of separating 

 and protecting the organism from the outer world, as is the case 

 in other groups; it also has the same function as the bones have 

 in vertebrates, that of skeleton. To the shell of the lobster the 

 body and leg muscles are attached as to the bones, and the separate 

 pieces of the shell are moveable on one another just as bones are. 

 On account of this function the skin must be hard like bones 

 (it consists of a substance called Chitin), and being hard it cannot 

 give and stretch as the body grows within. From this follows 

 that the crustacean can only grow by cracking its skin, or at 

 least the hard outer layer. When this occurs all the organs and 

 also the inner soft layer of the skin enlarge. The skin then forms 

 a new hard layer which serves as shell until the next moult. When 

 the time for moulting arrives, when, one might say, the lobster 

 is ready to jump out of the skin, the shell crackes at the hinder 

 end of the carapace and through this slit the animal works its 

 way slowly out. The back part comes out first and is followed 

 by the thorax and head, the whole being a tiresome and often 

 dangerous business since all limb-joints, the large claws, the eyes. 



