CRUSTACEA. 



141 



amount. New York, Boston, and Portland are the great markets for tin- 

 fresh lobsters, and in 1880 they handled 2,500,000, 3,637,000, and 

 2,000,000 pounds respectively. The total catch in that year was esti- 

 mated at 4,315,000 pounds in Massachusetts waters, and 14,234,000 pounds 

 on the coast of Maine ; having a total value, fishermen's prices, of $425,000. 



So far we have had nothing to sa}- of the physiology of the Crustacea, 

 but there are many interesting features connected with it, which may be 

 illustrated by the examples furnished by the lobster. Like the majority of 

 aquatic animals the lobster breathes by means of gills, — delicate mem- 

 branous outgrowths through which a transference of oxygen from the 

 water to the blood is easily effected. These gills are concealed under the 

 sides of the shell covering the interior part of the body, where, without 

 special provision, the supply of water would be rather limited. To obviate 

 this there is a broad plate in front of the gills which keeps constantly 

 moving back and forth, at each stroke pumping a supply of water over the 

 gills. 



Lobsters, like all other ten-footed crustaceans, are provided with ears 

 which are situated in the basal joint of the smaller feelers, or antennae, 

 shown in our plate. Each ear consists of a sac, closed on one side by a 

 thin membrane, and provided internally with a row of hairs, each of which 

 is in connection with a termination of a nerve. Inside of the cavity is a 

 fluid in which are several minute granules. Any vibration of the water is 

 communicated to the membrane, and this sets the granules in motion, and 

 these, in turn, hitting against the hairs, affect the nerves. The structure 

 is comparatively simple and doubtless has a very limited capacity. The 



Fig. 127. — Opossum-shrimp (M/jsis oculata), enlarged. 



opossum-shrimp, figured here, presents a peculiar condition in its auditory 

 apparatus, in that its ears are not near the head, but, on the contrary, are 

 in the tail, where they are just indicated by the oval marking in the cut. 

 This peculiarity recalls the fact that one of the relatives of the opossum- 

 shrimp is said to have, besides the normal organs of vision, accessor}' eyes 

 distributed along the sides of the body. 



We have already alluded to the fact that the Arthropods, at intervals, 

 molt the hardened integument. This with the lobster seems to be a serious 

 operation ; for, as the time approaches for the change of skin, the animal 



