EFFECTS OF LIGHT AND DARKNESS ON THE EYE 



523 



Text-fig. 1 A. Shows a retinula of the frog (left) and the retinula of Pro- 

 rhynchus (right). Three cytoplasmic regions are to be seen. Lines 1 and 1' 

 indicate the receptors or rhabdomes; line 2 connects the ellipsoid of a frog with 

 its analogue in Prorhynchus; lines 3 and 3' connect the myoid of a frog's retinula 

 with its analogue in the retinula of Prorhynchus. 



B. Two dark adapted retinulse of frog (left). Observe elongated myoid of 

 cone and contracted myoid of rod and no change in other cytoplasmic segments. 

 One dark adapted retinula of Prorhynchus (right). Anterior end to right. Note 

 the relative small size of the middle cytoplasmic segment and the low, trough- 

 like rhabdome. 



C. Two light adapted retinulse of frog (left). Observe contracted myoid of 

 cone and elongated myoid of rod; no change in other segments of the cytoplasm 

 of these cells. One light adapted eye of Prorhynchus (right). Observe absence 

 of middle segment of cytoplasm and the high, rounded rhabdome. The drawings 

 of rods and cones of frog taken from Arey ('16b). 



until the appearance of Arey's ('16) work that the authors of this 

 paper reahzed that the analogy, if not the homology, between 

 a visual element of a vertebrate and that of Prorhynchus was so 

 e\T.dent. Text figure 1 was made at the suggestion of Mr. W. H. 

 Taliaferro. 



This structural analogy suggested the problem of learning 

 whether or not there was to be found a functional analogy. 



