THE ORIGIN OF LIFE 75 



that the thought of the origin of the eye c gave him a \ 

 cold shiver. 



The first appearance of eyes dates very far back} 

 in geological time. In the lowest Cambrian rocks, 

 where, for the first time, we find a varied marine 

 fauna, there are crustaceans of the family of trilo- 

 bites with eyes, while there are others in which eyes! 

 are not present, or have not been detected. This is&quot; 

 parallel with the fact shown in the results of the 

 dredgings of the Challenger, that in the deep sea at 

 present there are some crustaceans furnished with 

 very large eyes, to suit the dim light of the ocean 

 depths, while others living in similar depths are 

 destitute of eyes. Here we have two remarkable 1 

 facts. First, that in the oldest seas, as well as now, 

 some crustaceans possessed eyes, while others appar 

 ently living in similar conditions were not so endowed. 

 Secondly, that, so far as known, the eyes of the oldest 

 crustaceans were as complete as those of their modern 

 relatives and on the same plan. With reference to 

 the last statement it is necessary to mention that the 

 eyes of the compound or facetted type which we have 

 in modern crustaceans and insects, and which are 

 of remarkably complex structure, are the oldest known 

 to us. Burmeister long ago showed that the eyes of 

 the ancient trilobites must have possessed all the 

 apparatus found in those of their modern successors, 

 and I have myself seen under the microscope eyes of 

 trilobites of the genus PJiacops in which the remains 



