22 THE EYE IN EVOLUTION 



from the Protozoa to the chordate Fishes ; it is a phenomenon which will be 

 discussed in greater detail later. ^ It is well known that in most animal species 

 the reaction appears intermittently in response to various stimuli, light having 

 a general inhibitory effect, sometimes directly by destruction of the photogenic 

 material in the light-producing cells, sometimes indirectly, acting through a 

 central regulatory mechanism, hormonal or nervous (Harvey, 1925 ; Heymans 

 and Moore, 1925 ; Moore, 1926). In the present connection it is interesting to 

 remark that in a number of species there is a daily rhythm in the capacity to 

 luminesce, a phenomenon seen even in unicellular Dinofiagellates (Harvey, 

 1952); and in some types of Insects ^ and perhaps in some jellyfish^ and a 

 balanoglossid * the rhythm may persist for several days so that the animal 

 will light up at the normal time of the day even if kept in constant 

 darkness. 



A final expression of diurnal, khythmicity is seen in the time -memory 

 OF SOME AUTHROPODS AND BIRDS. This curious and interesting phenomenon 

 was first demonstrated in bees by von Stein-Beling (1929-35) who showed that 

 within a cycle of 24 hours bees could be trained to visit an artificial feeding 

 station at regular occasions throughovit the day, a habit which could not be 

 maintained if an attempt were made to operate within a cycle greater or less 

 (e.g., 19 hours) than the normal solar diurnal rhythm. This ability has since 

 been verified by a number of observers ^ and it has been confirmed in wasps ® 

 and ants ^ as well as in the Amphipod Talitrus.^ So far as honey -gathering 

 insects are concerned it is probably connected with the hours at which flowers 

 periodically offer their nectar, but other activities are also involved. Thus 

 Kalmus (1935) found that if larvae and pupse of Drospohila — an insect which 

 normally emerges from its pupa before dawn — were kept in darkness during the 

 daytime and artificially illuminated for 3 consecutive nights, the flies emerged 

 in the evenings, remembering the time of the artificial dawn even although kept 

 in perpetual darkness. Such time-keeping mechanisms or " internal clocks " 

 are of wide occurrence, keeping time automatically with considerable precision, 

 but regularly set and kept in pace by light stimuli. It would seem that the 

 rhythm is influenced metabolically since it can be retarded by low temperatures 

 (under 5° C, Kalmus, 1934) or by drugs ; thus Grabensberger (1934) found that 

 by feeding quinine to trained bees, arrival at the sources of food was retarded, 

 while it was accelerated by iodothyroglobin. 



A similar apparently innate time-sense can be deinonstrated in some Birds, 

 which we will see ^ assvunes considerable importance in their extraordinary 

 ability to navigate over long distances. Thus Stein (1951) found that passerine 

 birds could be trained to coqie to feed at a particular hour each day provided 

 only that a 24-hour cycle were maintained, an acquirement retained for some 

 considerable time although the birds were kept in constant illumination or had 

 irregular feeding times ; experimental exposure to irregular periods of light and 

 darkness, however, tends to disorientate this sense when it is used as an aid to 

 navigation (Matthews, 1953-55). 



1 p. 736. 



2 Such as the firefly, Photinus—Bxic'k (1937). 

 ^ Pelagia — Heymans and Moore (1924-25). 



* Ptychodera—CrozieT (1920). 



5 Wahl (1933), Kalmus (1934-54), Kleber (1935), v. Frisch (1937), and others. 



6 Verlaine (1929). 



' Grabensberger (1934). 



8 Pardi and Papi (1952-53), 



« p. 63. 



