22 TEANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



the cones and the pigment which form the receiving 

 surface for the light are found to be different in the two 

 cases.* Engelmann discovered, that the stalks of the 

 cones exposed to light shorten, and that the pigment 

 cell processes stream down deeper into the retina. The 

 distinguished physiologist, who ascertained these changes, 

 guarded himself against the fallacy of a too sweeping 

 inference. He ascertained whether it was necessary that 

 the light should reach the retina to produce the effect. 

 For this purpose, the head of the frog was enclosed in an 

 absolutely light-tight bag, and light was allowed to shine 

 on the skin of the body. The wisdom of such an experi- 

 ment was justified by the result. A similar definite 

 change, but less in amount, was found, although the light 

 could not enter the eye, and could not therefore act 

 directly upon the retinal epithelium. 



Now the skin is well known to be sensitive to light, as 

 is shown by the changes this produces in its pigmentation. 

 The discovery, therefore involves more than appears at 

 first sight, but I need hardly say that it is, on that account, 

 still more important. 



Concluding Kemaeks. 



All these instances show us how pointless is structure 

 apart from function, and how baseless and unstable is 

 function apart from structure, and make in my judgment 

 an irresistable argument for the simultaneous examination 

 of both. 



Why is not such an examination more widely carried out 

 in Zoology ? Is it not because of that judicial separation 

 between comparative anatomy and physiology, which, as 

 was pointed out early in this address, is largely due to 



* Engelmann. Pfliigers Archiv. , Vol. XXXV, p. 453. 

 Nahmmacher. Physiol. Labor. Utrecht (1893). 



