rUBERC'LED GALENK. (.Mem aors&lu,. 



SMOOTH GALEN E.Galcue ocltiodes. 



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

 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 mois- 

 ture 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 ubmerged for any considerable time they will be drowned, 

 though more slowly, yet as certainly, 113 a human being under similar circumstances, the 

 gills being made for aerial respiration. In other land crabs, there are masses of membra- 

 nous 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 inod&s 

 hurtful to the respiratory functions. In the first place, all such membranes fail to 

 discharge their functions when they become dry, a familiar example being found in the 

 delicate membrane that lines the lips ; and, in the second place, as soon as the folds of 

 the branchias 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 coloured gelatine and placed under a gool 

 microscope, such a wonderful apparatus of interlacing vessels is observed as to baillo 

 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 branchiopoda, 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 TUBEECLED GALENE, so called from the 

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

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



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