FUNCTION OF PINEAL EYES 



105 



as yet unknown cells in the brain, even after the paired and pineal 

 eyes have become specialized for light reception. The whole study is 

 of special interest as showing the stages by which the eyes may have 

 been evolved. Higher fishes also show the power of responding to 



PINEALS REMOVED 

 1 



rm — 1 1 1 1 1 1 1 1 1 1 M 15. 



I I I i I I I I 1 ! ! I I I I II 1 I I II I I 



\t up 



hi 



Y f 



15 20 25 30 I S 



I I M I I I I I I I I I I I I I I I I I I I I I I 



DECEMBER JANUARY 



2S26 

 I I 



17 



nil 



10 15 ■ 

 ' '' 1 1 1 1 1 1 1 1 



MARCH 



Fig. 67. Colour-changes of larval lampreys, measured by the melanophore index (see 

 p. 300). Animals kept out of doors except as shown along the line AB, where rect- 

 angles above the line show illumination with electric light and below the line total 

 darkness. Normal animals show a regular daily rhythm, becoming pale at night. 

 Reversal of normal day and night illumination stops the change. On 19 December 

 the pineal eyes were removed from five out of the ten individuals and these there- 

 after remained dark (upper chart); the other five continued to show the normal 

 rhythm, until placed in total darkness. (After Young.) 



changes of illumination after the paired eyes and epiphysis have been 

 removed (p. 210). 



If the pineal eyes are not essential for the initiation of movement, 

 what is then their function ? In the ammocoete larva there is a daily 

 rhythm of change of colour, the animals becoming dark in the day- 

 time and pale at night. After removal of the pineal eyes this change no 

 longer occurs: the animals remain continually dark (Fig. 67). This 

 effect on the colour is produced by the action of influences from the 

 pineal, passing to the pituitary gland (see p. 103). It seems that 

 the pineal apparatus is an organ concerned with adjustment of the 

 internal activities of the animal to correspond to the changing con- 

 ditions of illumination. The control may be effected by impulses 



