6680 



Crustacea. 



fresh mussel, he gluttonously endeavoured to bolt ; but it was too 

 large and too thick ; he got one half into his stomach, but the other 

 he could not get into his mouth ; he struggled and pulled and tugged 

 in vain ; the piece was too large to swallow, and his mouth was so 

 widely stretched that he could not bite it in two ; so he tried to pull 

 it back again, but failed to do so, pull and tug as much as he would. 

 He tried and tried in vain ; and repeated failures evidently produced 

 alarm. His eyes began to stare, and he tossed about his arms. He 

 raised himself upon his hind feet, and, beating the water with the 

 others, he ran away erect. He strained himself to that extent that 

 he fell upon his back a struggling, choking crab ! and if he had not 

 been already green, he would most assuredly have gone black in the 

 face. He was in such a fright ! I came to his rescue, and pulled 

 the piece of meat from his greedy mouth, to his great comfort and 

 greater relief. He took care not to eat so fast again, and to bite meat 

 before he swallowed it, all the rest of his life, unless a crab is like 

 some individuals among a higher order, who never learn by ex- 

 perience. 



The crab is not a daily feeder; few carnivora are. Having satis- 

 fied his appetite, the greatest dainty may live in peace within his 

 reach, as a nipper-crab of Mr. Couch's did with a Montagu's sucker 

 for several days, although it fell a prey to him at last. 



The stomach in Crustacea is very complicated. It is formed for 

 grinding up the food. Three calcareous plates, with serrated surfaces, 

 meet together at a common point, and do the work of mastication. 

 Digestion then goes on, and the altered food mixes with the bile as 

 it passes out of the stomach, when it is ready to be taken up as a 

 repairing-supply to meet the general wear and tear of the tissues of 

 the body. 



The stomach differs not much in Crustacea generally ; it is more 

 strong, and with calcareous plates and teeth, in the larger kinds, but 

 has ciliated plates and fine hairs in the smaller and weaker forms. 



The mouth of the crab is protected by several pairs of limbs that 

 overlie the mandibles, and the outermost are formed into a broad 

 operculum that encloses and protects the whole. In the lobster and 

 prawn the operculum is less perfect, and the leg-like character of the 

 appendages more apparent. This increases the lower we proceed, 

 until the leg is developed in all its proportions, as seen in the Edri- 

 ophthalmic Crustacea, where there are present two pairs more than 

 belong to the higher types. The Gnathopoda, which in the higher 



