202 CARNEGIE INSTITUTION OF WASHINGTON. 



Fishes and cephalopods have independently developed eyes the mechanical 

 principle of whose construction is essentially the same. One is entitled to 

 suppose that in the two cases this is due to common adjustment to the same 

 undertying reahty, the nature of light and its mode of operation. The com- 

 bination of lens, dark chamber, and sensitive surface is one of the most 

 efficient, if not quite the most efficient, system upon which an image-forming 

 eye might be constructed, of which fact fishes and cephalopods, so to speak, 

 bear independent witness. 



Similar adjustment to underlying reality of some sort msiy be inferred with 

 justice wherever convergent evolution occurs with respect to characters which 

 there is real reason to believe are of service to their possessors. Much evidence 

 has already been presented^ tending to show that the coloration of fishes at 

 least is obUterative in effect. It therefore seems fair to conclude tentatively 

 that the convergent evolution of fishes and some cephalopods in respect to 

 pattern-display indicates the existence of laws of optical illusion to which the 

 color-patterns of animals tend to conform. 



The hypothesis that fishes, for example, have in course of time become 

 obliteratively colored through natural selection, involves the assumption that 

 they are preyed upon by other animals of more or less keen powers of dis- 

 crimination habitually exercised. Hence preliminary experiments were under- 

 taken with the object of determining to what extent a fish of such apparent 

 intelligence as the gray snapper might conceivably exert bionomic pressure 

 to modif}^ the color or form of fishes or Crustacea among which it lives and 

 upon which it feeds voraciousl3^ The time available for tliis work was so 

 strictly limited, however, that while the results obtained are interesting, they 

 are of present value chiefly as they suggest promising modes of attack upon 

 the problem. 



When the weather permitted, the work of photographing the fishes in their 

 natural surroundings through use of diving apparatus and camera specially 

 fitted for submarine work was continued with most gratifying results. Twenty 

 additional pictures were secured showing fishes characteristically engaged, 

 the detail in a number of which is scarcely to be surpassed in photographs 

 taken on land. 



The Effect of Anesthetics on Basal Metabolism, by J. F. McClendon. 



Owing to the difficulties in keeping metabolism down to the basal level in 

 higher animals, comparative studies in metabolism upon forms in which this 

 can be done are desirable. In choosing an animal for such investigations, the 

 jellyfish Cassiopea xamachana was decided on, since the automatic activity 

 of the nervous system may be abolished by cutting off the margin of the bell 

 and the respiration-rate is independent of oxygen tension, except for very 

 low tensions of oxygen. 



In determining the rate of metaboUsm, 4 jelly-fish of large size (up to 15 cm. 

 diameter) were deprived of manubrium and bell-margin and placed in sea- 

 water in an air-tight jar of about a liter capacity and rotated in a thermostat 

 at 30° for 1 hour. The oxygen used was determined by the Winkler method 

 and the CO2 given out was calculated from the alkaline reserve and changes 

 in the hydrogen-ion concentration (expressed as Ph). It was found that the 

 neuro-muscular system in the bell was anesthetized with 0.5 per cent ether in 

 sea-water, whereas the jelly-fish died at the end of 1 hour in 3 per cent ether 

 and in less than an hour in 4 per cent ether. The respiratory quotient was 

 found to be about 0.95, and since the CO2 determinations were less accurate 



1 Journ. of Exp. Zool., Aug. 1917, and previous reports in this Year Book. 



