No. I.] EVES OF MOLLUSCS AAFD ARTHROPODS. 89 



essential, light-sensitive elements. If this also be true, it must 

 of necessity follow that by far the majority of compound eyes 

 are not adapted for ^^ mosaic vision" as commonly understood, 

 but for the perception of inverted images formed by the corneal 

 facets upon the crystalline cones. 



I also claimed, on theoretical grounds, that neither the om- 

 mateum nor the retina of Arthropods could have arisen as an 

 outgrowth of the brain, and I may add that my recent observa- 

 tions on the development of the eyes of Vespa have confirmed 

 this conclusion. 



Certain facts in the anatomy and distribution of the simplest 

 kinds of eyes, as well as other sense-organs, lead me to suppose 

 that their function was originally not that of sense-organs ; that 

 is, organs by means of which their possessor became cognizant 

 of changes in external conditions ; they were rather the receivers 

 and transmitters of external changes which had in themselves a 

 stimulating and beneficial effect upon the organism. The con- 

 stant association of certain sensory impressions with changes 

 in external condition finally led to the so-called " recognition " 

 of such changes, and the organ which recorded those changes 

 then became a true sense-organ. This supposition may explain 

 the multiplication of highly complicated " sense-organs " in 

 animals which can apparently make no use of so many to per- 

 ceive objects. The great number of sense-organs present in 

 some animals is intelligible when we assume that they have a 

 phagous function ; and as, on any supposition, they are especially 

 affected by changes in external conditions, I have called them 

 Dynamophagous organs. 

 Milwaukee, April n. j 



