326 CONTRIBUTIONS TO THE NATURAL HISTORY 



unless the fleshy parts are fully expanded, shows plainly that here again there is an 

 intimate connection between respiratory movements and locomotion. In Cephalopoda 

 this is still plainer, for, from the form of the respiratory cavities, from the disposition of 

 the sacs in which the gills are placed, we can easily infer that the contractions and 

 dilatations of these sacs, by which the water is renewed, must afford a material me- 

 chanical assistance in the progress of locomotion. Again, throughout the type of Articu- 

 lata, this connection is most intimate, the respiratory organs being directly connected 

 with the locomotive appendages, forming, indeed, parts of the various kinds of oars, 

 fins, legs, and chewing appendages, by which the principal motions of the body are 

 sustained. Not a joint can be moved here without influencing respiration, and, again, 

 the expansion and contraction of the respiratory cavities, the filling of the respiratory 

 vesicles, or the large circulatory sacs connected with the gills or fins, and the introduction 

 of air into the tracheal tubes, must, in their turn, influence locomotion. And it were a 

 subject well worthy of the attention of physiologists, to trace more minutely this double 

 connection throughout the animal kingdom. Perhaps the type of Articulata is best 

 adapted to make a beginning in these investigations. For among them, in the Crustacea, 

 for instance, the chewing of the food itself is directly connected with the jirocess of 

 respiration. The motion of the jaws aids in forming and maintaining a regular current 

 of water along the gills through the respiratory cavities, and even when otherwise not 

 employed, the jaws are kept in motion in some degree to assist respiration. And it can 

 hardly be doubted that the process of respiration also materially aids the insects in 

 their flight, and that the state of expansion or contraction of the respiratory cavities 

 is very different in the state of repose, or during flight. While watching locusts, I 

 have often been struck with the state of wide expansion of their abdomen at the 

 moment they start, and with the collapsed state of the whole body soon after they 

 have alighted, which is even so great as to prevent their rising again immediately 

 when chased. 



Again, among Vertebrata, we find in fishes that the respiratory movements — the 

 lifting and shutting of the operculum, the filling and emptying of the branchial cavity — 

 aid the fish in slowly progressing ; so much so, that when resting upon the bottom of a 

 glass jar, apparently immovable, these animals are at times suddenly propelled forward 

 under the action of a powerful occasional contraction of the branchial cavity, even if the 

 ordinary locomotive organs, the tail and fins, remain absolutely quiet. How close a con- 

 nection exists between locomotion and respiration in the Ichthyoid Batrachians, I have 

 often had occasion to witness in a Proteus kept in confinement, in which the gills grew 

 gradually paler and paler if the animal was absolutely motionless, but would instantly be 



