94 



THE EYE IN EVOLUTION 



In it, the eyes are the sole photoreceiDtors and their occhision or section 

 of the optic tracts inhibits all normal responses (Atzler, 1930) ; but 

 the fundamental role of hormonal control is seen in the fact that 

 transplanted portions of integument react normally long before nervous 

 connection can be established (Janda, 1936). On the other hand, in 

 the grasshopper, Acrida turrita, some colour changes (adaptation to red, 

 orange, yellow and violet) are said to occur after the eyes are totally 

 varnished, while a green colour can be developed only if the eyes are 

 functioning (Ergene, 1952). 



Among CRUSTACEANS the vividly dramatic colour changes are 



'•:2?* 



I' *r' / 



4 



-Colour Changes in Crustaceans. 



The three shrimps (Crago) were initially coloured alike, as the specimen 

 on the left. This was used as a conti'ol and showed no change after an injection 

 of sea-water. That in the centre was injected with an alcohol-insoluble fraction 

 of the commissures ; that on the right by a total water-soluble fraction of the 

 commissures (Brown and Klotz). 



Prawn 



entirely mediated by hormones elaborated in the cephalic neuro- 

 secretory system. 1 That a blood-borne agent was the responsible 

 factor was first demonstrated by Roller (1925-30) who found that the 

 colour of a lightly coloured shrimp, Crago vulgaris, could be altered by 

 blood transfusion from a darkened specimen. Perkins (1928-32) 

 thereafter discovered in the prawn, Pakemonefes, that denervation of a 

 region had no effect on colour responses while occlusion of the blood 

 supply inhibited them ; he also demonstrated that injection of an 

 extract of the sinus gland induced blanching in a blinded animal while 

 removal of the eye-stalks resulted in the assumption of a permanently 

 darkened appearance. These early results have been amply confirmed 

 and it would appear that the intricate control of the chromatophores of 

 Crustaceans is effected by at least two and sometimes three or four 



^ See further p. 554. 



