CoNGDON, Reactions to Light. 323 



PISCES AND AMPHIBIA. 



Certain work upon the compensatory movements of vertebrates has already been 

 referred to while discussing existence of phototaxis in binocular vision. The atten- 

 tion of several workers has also been recently given to locomotor light responses of 

 fishes and amphibians, in particular those dependent upon the light sensitiveness 

 of the skin. Previously a few amphibians were known to possess this dermal 

 function and blind newts of the genus Triton had been found to collect in the shade. 



Two primitive vertebrates, Amphioxus and the larval lamprey, have been exam- 

 ined by Parker ('05, '06) with the resuhing discovery that both can perceive light 

 through the skin. Amphioxus is phototactic and negatively photokinetic. The 

 larval lamprey has these same characteristics. It is somewhat startling to learn that 

 the latter animal orients even when the head is removed. The especial sensitiveness 

 of the tail to light is correlated with a habit of burrowing head first until the rest of 

 the body is covered. The earliest study of the orientation of blind fishes in response 

 to light was made by Eigenmann ('00) upon Ambylopsis. Payne ('07) has within 

 the year repeated and extended Eigenmann's observations. The animals gather 

 in shade by some other process than direct orientation. They give a stronger re- 

 sponse under vertical than under horizontal illumination. A photokinetic effect 

 seems to be present along with movements suggesting discomfort. The experi- 

 ments employed are simple and not devised to carry very far the analysis of the com- 

 plex nervous activities of the animals. 



Parker ('03) demonstrates the occurrence of phototaxis for blind amphibians 

 by means of frogs whose optic nerves have been severed. The animals can orient 

 promptly, but only occasionally do they move toward the light. If the skin of a 

 normal animal be covered orientation takes place readily by means of the eyes. 



ToRELLE ('03) concerns herself with the behavior of the frog without reference 

 to the relative activities of eyes and skin. Orientation is tested in certain experi- 

 ments by placing the frog in a box 12 in. long with a glass window 9 in. wide and 5 

 in. high. It may be objected to this procedure that the animal was presented with 

 a pattern of light and shade whose image possibly covered only a portion of the 

 retina at once. The only type of phototaxis which could be inferred from orienta- 

 tion toward the window was that variety present in all binocular vision. The other 

 methods employed by Torelle are not thus open to criticism, and her conclusions 

 are well established. She, as well as Parker, finds that orientation to light fre- 

 quently takes place without locomotion. If one eye be covered the animal orients 

 obliquely to the light when at rest. In spite of this fact it goes directly toward the 

 light as did Ranatra when so blinded. When an individual is put in direct sunlight 

 it will do one of two things. If there is a possibility of its walking into the shadow 

 without losing its orientation to the sun it is likely to do so, but frequently it varies 

 the process by hopping into the shadow and then turning around so as to come to rest 

 with its head toward the light. The field toward which the animal will orient for the 

 time being is thus chosen in the same manner as Cole describes for certain insects. 

 Some features of the frog's response are more mechanical than those we have just 

 been considering. While sitting facing the light it may be made to raise or depress 

 its head in an effort to keep its alignment with the rays if their angle of incidence 

 upon it be changed. The behavior of the animal at low temperatures is probably 

 related to its hibernating habit. Below 10° C. in air it becomes negatively photo- 



