258 



characteristic of his whole criticism, has magnified the evident inter- 

 change of the word lateral for median into a gigantic mistake. 



4) Prof. Lankester, in commenting on my statement that «the 

 amount of energy absorbed by a heliophagous organ would depend 

 upon the most perfect condensation of light upon a given area«, in- 

 sinuates that I had no time to learn from some text-book the self 

 evident fact that a lens can concentrate only those rays of light which 

 fall upon its surface! Therefore, he adds, there is no necessity for a 

 lens, according to my supposition, for a naked surface equal to that 

 of a lens would absorb more light than would a retina with a lens in 

 front of it. If my observations on the arrangement of nerve fibres are 

 correct, it follows that it is necessary to regulate the direction of the 

 rays of light; the lens is an important factor in bringing this result 

 about. Moreover Prof. Lank es ter s objection rests upon the supposi- 

 tion that the surface of the retina, is as large or larger than that of the 

 lens. There are some cases, however, in which the surface of the 

 retina is considerably smaller than the surface of the lens. 



Prof. Lankester declares that a »naked epidermic surface of an 

 area equal to that of a lens would present a perfect instrument for the 

 absorption of solar energy«, I have mentioned in my paper upon the 

 »Eyes of Molluscs and Arthropods(f numerous instances of just such 

 «perfect instruments^ as he describes. 



5) On p, 291, Prof. Lankester describes another »melancholy 

 instance« of Dr. Patten's unwarrantable adhesion to theory in the 

 face of opposing facts«, in supposing that the lateral eyes of Scorpion 

 and Limulus were provided with a vitreous body. I had good reasons 

 for making that supposition, and in the case of Scorpions I had the 

 authority of Grabe r as opposed to that of Lankester. It is not 

 strange that my acceptance of Grab er s statements should strike Prof. 

 Lankester as a »melancholy« adhesion to theory. Indeed it must 

 appear very »melancholy« now that B ertkau has also seen fit to doubt 

 the accuracy of Prof. Lankester s observations on this point! 



6) My criticism of Prof. Lankester's assertion that mesoblastic 

 pigment cells were present in the ommateum of faceted Arthropod eyes, 

 as was expected, met with scanty approval. I stated my objections to 

 Prof. Lankester's hypothesis; in my opinion, his criticism does not 

 in the least invalidate those objections. Prof. Lankester found a few 

 branching pigment cells in the eyes of Scorpions, and concluded that 

 they were of mesodermic origin, and forthwith divided Arthropod eyes 

 into autochromic and exochromic. 



Prof. Lankester now seeks to support his supposition that 

 mesodermic pigment is present in the ommateum of the compound 



