AQUATIC RESPIRATION. 2i)i) 



belonging to the respiratory system are exten- 

 sively distributed over the whole surface of these 

 filaments. Organs of this description are deno- 

 minated Bra7ichi{B, 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 branchial veins. 



The larger Crustacea have their branchiae 

 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 

 are only seven on each side. To these organs 

 are attached short and flat paddles, which are 



* Page 269 of this volume. 



