94 RESPIRATION AND LOCOMOTION. 



and hard, you perceive, beneath the skin. That is the dorsal 

 plate or gladius of the Cuttle-fish, the well-known " pounce-bone " 

 that you see about on the sand, and in the druggists' shops. If 

 you are not over fastidious, and have a mind to turn dissector for 

 once, your penknife will readily lay open the Cuttle-fish and 

 show you the " bone " in its natural position, where it protects 

 the vital organs, and at the same time serves, by its light and 

 buoyant character, as a sort of float to aid the animal in its 

 vivacious movements in the water. The common Cuttle-fish is 

 the only Cephalopod that has this internal float, although in the 

 common Calamary, or Squid, there is a thin and flexible cartila- 

 ginous plate in the form of a feather, which equally answers the 

 purpose of defence, and also aids in locomotion. 



Now, look at the mouth of the sack, where the head protrudes, 

 and you will see projecting, just beyond the opening, the end of 

 a tube or pipe, which, if the dissection be proceeded with, will be 

 seen to be the mouth of a funnel-shaped structure, connected, in 

 the interior of the body, with the branchise or breathing organs. 

 These branchiae are lodged in hollow cavities or chambers, and 

 communicate with the surrounding water by valves, through 

 which the fluid is admitted to aerate the blood, by the dilatation 

 of the muscular investment of the body. When, however, the 

 purpose of respiration has been effected, and the water has to be 

 got rid of from the branchial chambers, the valves through which 

 it entered refuse it egress, and it has to be forced out through the 

 funnel smartly or slowly, as the animal may choose. Now, 

 observe : if the Cuttle-fish exerts but little pressure, and ejects 

 the water slowly, all is well the chambers are emptied, again 

 refilled, and respiration goes on without stir or commotion. But 

 if, on the contrary, the muscular investment be suddenly and 

 violently contracted, the water is then made to rush out of the 

 funnel in a violent jet, while the Cuttle-fish, by the mere reaction 

 of the surrounding medium, shoots backward through the water, 

 on the same principle, and with almost as much rapidity, as a 

 rocket mounts into the air. In the same manner all the Cephalo- 

 pods, naked and shell-bearing alike, dart along through the 

 water, repeating the movements at pleasure, with intervals be- 

 tween, or in quick and continued succession ; and thus beauti- 

 fully, by one and the same contrivance, is the double puqxtse 

 effected of respiration and rapid locomotion. Moreover, as these 



