AQUATIC RESPIRATION. 299 



action of the aerated water, the immediate organs 

 of respiration consist of long, narrow filaments 

 in the form of a fringe, and the blood-vessels 

 belonging to the respiratory system are exten- 

 sively distributed over the whole surface of these 

 filaments. Organs of this description are deno- 

 minated Branchice, or Gills; and the arteries 

 which bring the blood to them are called the 

 branchial arteries; the veins, which convey it 

 back, being, of course, the hranchial veins. 



The larger Crustacea have their branchiaB 

 situated on the under side of the body, not only 

 in order to obtain protection from the carapace, 

 which is folded over them, but also for the sake 

 of being attached to the haunches of the feet- 

 jaws, and thoracic feet, and thus participating in 

 the movements of those organs. They may be 

 seen in the Lobster, or in the Crab, by raising 

 the lower edge of the carapace. The form of 

 each branchial lamina is shown at g, in Fig. 

 354* : they consist of assemblages of many 

 thousands of minute filaments, proceeding from 

 their respective stems, like the fibres of a feather ; 

 and each group having a triangular, or pyra- 

 midal figure. The number of these pyramidal 

 bodies varies in the different genera ; thus the 

 Lobster has twenty-two, disposed in rows on 

 each side of the body ; but in the Crab, there 



* Page 269 of this volume. 



