THE TUBERCLED GALENE. 



579 



should be kept in a moist state. Even in the land crabs, which pass nearly the whole of 

 their time upon the dry ground, the gills need moisture, and are constantly maintained 

 in their wet condition by an internal chamber which is filled with water and supplies 

 moisture to the branchiae. This structure is analogous to that of the breathing organs 

 in the climbing perch and other land-visiting fish, which have already been described 

 in an earlier part of this volume. In order to retain a full supply of water, the land 

 crabs are forced to visit a stream or pond daily, but a single dip is sufficient for the 

 twenty-four hours. It is very remarkable that these particular crustaceans cannot endure 

 total immersion in water, and that if they are submerged for any considerable time they 

 will be drowned, though more slowly, yet as certainly, as a human being under similar 

 circumstances, the gills being made for aerial respiration. In other land crabs, there 

 are masses of membranous folds, and in some is found a spongy mass in which the 

 needful water is stored. The drying of the branchial membranes produces a double 

 effect and is in two modes hurtful to the respiratory functions. In the first place, all 

 such membranes fail to discharge their functions when they become dry, a familiar 





TUBERCLED QALENE. Qalene dorsalls. 



SMOOTH QALENE. Go/cue ochtodes. 



example being found in the delicate membrane that lines the lips ; and, in the second 

 place, as soon, as the folds of the branchiae begin to dry, they collapse, and so diminish 

 the extent of surface which is presented to the air. 



The gills may be easily examined on opening a crab or a lobster, in which animals 

 they are popularly called " lady's fingers." Even to the unassisted eye they exhibit 

 great beauty of structure, but when injected with colored gelatine and placed under a 

 good miscroscope, such a wonderful apparatus of interlacing vessels is observed as to 

 baffle description, and almost to elude the most delicate pencil. Some of the lower 

 crustaceans have a very curious system of respiration, of which the organs of locomotion 

 are essential portions, and in allusion to this peculiarity, the creatures are called bran- 

 chiopoda, or gill-footed crustaceans. 



ON the accompanying illustration are two figures representing two dissimilar species 

 of the same genus. The left-hand figure is the TUBERCLED GALENE, so called from the 

 profuse warty excrescences which grow upon the claw-feet and the pincers. The right- 

 hand figure is the SMOOTH GALENE, in which the claws are very much smaller in 



