226 CTENOPHORiE. Part II. 



is an intimate connection Ix'twcen respiratory movements and locomotion. In 

 Cephalopoda this is still plainer ; lor, from the form of the respiratory cavities, and 

 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 mechanical assistance in the progress of loco- 

 motion. Again, throughout the type of Articulata this connection is most intimate, 

 the respiratory organs being directly connected with the locomotive appendages, and 

 forming, indeed, part 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 con- 

 traction 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. It is a 

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

 double connection throughout the animal kingdom. Perhaps the type of Articu- 

 lata is best adapted to make a beginning iir these investigations. For among 

 them, in the Crustacea for instance, the chewing of the food itself is directly 

 connected with the process 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 not otherwise employed, the jaws are kept in motion in 

 some degree to assist respiration. And it can hardly be doubted, that the jirocess 

 of respiration also materially aids the Insects in their flight, and that the degree 

 of expansion or contraction of the respiratory cavities is very different in the state 

 of repose or during flight. While watching grasshoj^pers I have often been struck 

 with the wide expansion of their abdomen at the moment of starting, and with 

 the collapsed condition 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 res2:)iratory movements — 

 the lifting and shutting of the opercuhnn, 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 sud- 

 denly propelled forward imder the action of a powerful occasional contraction of 

 the branchial cavity, even though the ordinary locomotive organs — the tail and fins 

 — remain absolutely quiet. How close a connection exists between locomotion and 

 respiration in the Ichthyoid Batrachians, I have often had occasion to Avitness in 

 a Proteus kept in confinement, in which the gills grew gradually paler and paler 

 when the animal was absolutely motionless, but would instantly l^e filled with a large 

 quantity of blood and appear intensely red after some violent motion. It might 

 be objected, that this is a mere influence of locomotion upon circulation ; but if 



