io6 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



ward, i. e., upward, and finally has penetrated to the 

 superior surface, so that both eyes are on one side. This 

 peculiarity would be incredible, if we did not know of 



1 



its existence, and is an illustration of the extraordinary 

 powers of accommodation possessed by nature. The 

 Heterosomata (flatfishes) can only be considered a de- 

 generate group. The scyphobranch line presents a 



