THEORY OF SEX-DIMORPHISM 91 



has no meaning except in the female. Unless 

 indeed one supposes that both sexes used to 

 carry the eggs, or that the ancestors of 

 Argonauta were hermaphrodites but for any 

 such hypotheses, there are no bases. 



Let us take one of those very interesting 

 cases where the female has something definite 

 and positive which the male has not the 

 frog Nototrema with its dorsal pouch in which 

 the eggs are carried. Is there any warrant 

 for supposing that this was once a specific 

 character? Another case in point may be 

 found in the so-called claspers of male 

 Selachians. In a fish like the skate they are 

 very conspicuous sex-characters ; they are 

 highly specialised structures with complicated 

 musculature and skeleton. They are very 

 definitely male organs, without any representa- 

 tion in the female. There is no warrant for 

 supposing that the ancestors of our modern 

 Selachians had structures like these claspers 

 in both sexes, or even rudiments of them. 



Again, in most mammals, though the ovaries 

 always remain internal, the testes are carried 

 in an external pouch or scrotum into which 

 at a certain stage of development they 

 descend, as it were by a rupture normalised. 

 This is a definite male peculiarity, a specialisa- 

 tion not necessarily present ; it is not hinted 

 at in the female ; and again there is no warrant 

 for regarding it as a transformation of any 

 specific character ever common to the two 

 sexes. In the same way the protruding egg- 

 sacs of many female water-fleas, e. g. Cyclops, 

 are extra things on the female's part. 



DIFFICULTY AS TO ORIGINS. Darwin's 



