Eyes of MoUuscs and Arthropods. 543 



complex of activities is far less intricate, is provided with nearly fifty 

 times as many! It is absurd to supi)Ose that these inactive creatures, 

 with hardly a trace of the higher animai functions, should ne ed a hun- 

 dred eyes. But if they are not necessary , how could they have been 

 developed by naturai selection ? Eveu supposing them once developed, 

 they must be an enormous vital expense for which the animai gets no 

 return. Itiscontrary to ali our conceptions of evolution, to suppose that 

 these expensive organs can be long sustained without some beneficiai 

 return to the animai. But they must have developed once, and we may 

 be sure they did not spring into existence, Minerva-like, armed with ali 

 the functioual powers their complicated structures would indicate. What 

 factors, then, could force the development of these organs to their 

 present height, and sustain them there? That was the question which 

 first induced me to study these eyes more closely ; the facts related in 

 the following pages furnish, I believe, a partial solution to the problem. 



I desire to say a word in justification of certain statements, to be 

 made in the following paper , which may appear too dogmatical , or 

 without sufficient foundation in fact. lam, I believe, perfectly con- 

 scious of the uncertain ground upon which I tread. That my statements 

 concerning the originai function of the ommatidia, of the eye, and of animai 

 pigment, are positive, is just what I desired. Facts must be tested in two 

 ways : first, by Observation, and secoud, by their );touch-stone« proper- 

 tres. An Observation that explains nothing is no more a fact, thau an 

 explanation founded upon nothing. In this paper, I have attempted to 

 apply the same principio. I consider my observatious as worthless 

 without their «better halves«, the deductions. My observations have 

 been tested by their ability to support reasonable deductions. It is 

 not a theory that I have tried to make, uor observations, but to marry 

 theory to Observation, to obtain facts. 



Positive statements have been made for several reasons: first, for 

 the benefit of the reader, that he may iinderstand what I consider tobe the 

 signification of the observations; he may then reject, or accept them as 

 he sees fit; secondly, because, I believe, to weigh an Observation with 

 this and with that, and after a long discussion come to the conclusion 

 that we know nothing at ali about it, only burdens to no purpose the ai- 

 ready overladen literature, and might better have been left undone. 



I hope the reader will treat my deductions in the same spirit that 

 they were given, not as dogmatic statements, butas tests of ob serva- 

 ti ons. 



From the unsatisfactory results obtained by the study of Pecten 



