DIMORPHISM AND POLYMORPHISM 357 



in all sexually dinuvp/iic organisms the germ-plasm must contain 

 a varied number of double jirimary constituents of somatic char- 

 acters, — namely, those which represent characters which differ 

 in male and female individuals. These in the first instance con- 

 cern the organs in which the sexual cells are developed, nourished, 

 stored, and removed, — that is to say, the so-called sexual glands 

 and their ducts ; then follow the active and passive copulatory 

 organs, and the stmctures connected with oviposition ; and, 

 finally, special sexual characters arise with regard to the organs 

 for supporting and nourishing the offspring — such as mammary 

 glands, teats, and uterus, — or they may refer to the instinct 

 of carrying the eggs in the mouth, as in the male of a tropical 

 species of frog, or to that in the female butterfly, which deposits 

 its eggs in a definite manner on a certain plant. In the last two 

 instances, the structure of the body and the nerve-centres must 

 also be different in the two sexes, and the male and female type 

 of these parts must exist in a latent condition in every germ- 

 plasm. Under this head, moreover, ^secondary'' sexual cha?'ac- 

 te?'s must be included, such as the various tracking and alluring 

 organs of the males, the gorgeous colours of male birds and 

 butterflies, the scent-producing organs of the latter, which exhale 

 perfume, and the song of male birds and insects. 



In the human race we know that all the secondary sexual 

 characters are transmitted by individuals of the opposite, as well 

 as of the corresponding sex. A fine soprano voice, for instance, 

 may be transmitted from mother to granddaughter through a 

 son, and a black beard from the father to the grandson through 

 a daughter. And in other animals, the sexual characters of both 

 sides must be present in every sexually differentiated organism, 

 some of them becoming manifest and others remaining latent. 

 This fact can only be proved in certain cases, for we seldom 

 notice the individual differences of these characters with suffi- 

 cient accuracy ; it can, however, be shown to be true, even in 

 tolerably simply organised species, and we must therefore sup- 

 pose that latent characters belonging to the other sex are always 

 present /;/ each sexually differentiated organistn. In bees, the 

 males developed from unfertilised eggs possess the secondary 

 sexual characters of the grandfather ; and in the water-fleas, in 

 which several orenerations of females arise from one another, 

 the last of these generations produces males with the secondary 

 sexual characters of the species, which must consequently have 



