38 



RESPIRATORY MECHANISMS 



In the Cephalopoda and especially in the cuttlefish the two 

 feathery gills are located in the mantle cavity. Water is 

 taken in along the edge of the mantle, but the cleft can be 

 closed completely and the water driven out by a contraction 

 of the highly muscular mantle through the funnel. This 

 makes the respiratory movements serve also for locomotion 

 and establishes a close correlation between the rate of ventila- 

 tion and the muscular work involved in swimming. Winter- 

 stein (1925) measured ventilation and utilization in Octopus. 



VentiZa&orhseffeAt. 

 l/St. 



t,o T 



a,* 



Dyspnoe 



Jfupnoe 



jSauerstoffdruck. 



HX> 200 



Fig. 13. See text. (Lindroth.) 



300 

 mm Hg 



He found that oxygen lack would cause an increased ventila- 

 tion even to 10 times the normal. Increased carbon dioxide 

 at tensions below 6 mm would also cause an increase, but at 

 slightly higher tensions the respiration was inhibited. The 

 utilization may reach 80%, but Hazelhoff (1938) observed 

 an average of 63% in Octopus vulgaris. 



The most highly specialized and effective branchial ap- 

 paratus is that possessed by fishes. The gill filaments are 

 arranged on gill arches (Fig. 14) between the mouth and the 

 branchial cavity. As shown in Fig. 15, the gill filaments of 

 neighbouring arches are connected in such a way that all the 

 water passing between them cannot avoid a very intimate 



