22 HISTORY OF CRUSTACEA. CHAP. IV. 



In the first place, and before inquiring into its signi- 

 ficance, I will say a word upon this fact itself. It was 

 natural to consider whether two different species with 

 very similar females and very different males might not 

 perhaps live together, or whether the males, instead of 

 occurring in two sharply defined forms, might not be 

 only variable within very wide limits. I can admit 

 neither of these suppositions. Our Tanais lives among 

 densely interwoven Confervse, which form a coat of 

 about an inch in thickness upon stones in the neighbour- 

 hood of the shore. If a handful of this green felt is put 

 into a large glass with clear sea-water, the walls of the 

 glass are soon seen covered with hundreds, nay with 

 thousands, of these little, plump, whitish Isopods. In 

 this way I have examined thousands of them with the 

 simple lens, and I have also examined many hundreds 

 with the microscope, without finding any differences 

 among the females, or any intermediate forms between 

 the two kinds of males. 



To the old school this occurrence of two kinds of 

 males will appear to be merely a matter of curiosity. 

 To those who regard the "plan of creation" as the 

 "free conception of an Almighty intellect, matured 

 in the thoughts of the latter before it is manifested in 

 palpable, external forms," it will appear to be a mere 

 caprice of the Creator, as it is inexplicable either 

 from the point of view of practical adaptation, or 

 from the "typical plan of structure." From the side 

 of Darwin's theory, on the contrary, this fact acquires 

 meaning and significance, and it appears in return 



