76 PLAIN FACTS FOR OLD AND YOUNG 



tlie "union of two dissimilar elements. These elements 

 do not, in liiglier organisms, as in lower forms of life, 

 constitute the individuals, but are produced by them; 

 and being unlike, they are produced by special organs, 

 each adapted to the formation of one kind of element. 

 The two classes of organs usually exist in separate indi- 

 viduals, thus giving rise to distinctions of sex, an indi- 

 vidual possessing organs which form one kind of ele- 

 ment being called a male, and one possessing organs 

 for the formation of the other kind of element, a 

 female. The sexual differences between individuals 

 of the same species are not, however, confined to the 

 sexual organs. In most classes of plants and animals, 

 other sexual differences are very marked. In some of 

 the lower orders of animals, and in many species of 

 plants, the male and female individuals are so much 

 unlike that for a long time after they were well known, 

 no sexual relation was discovered. 



In some species of plants, as for example the pond 

 scums, there is apparently no distinction of sex; and 

 yet a union of two distinct individuals is necessary for 

 fecundation; and there is reason to believe that these 

 two individuals, though apparently in no way dissimi- 

 lar, presenting under the microscope complete identity 

 of appearance, are really sexually distinct, one being 

 male and the other female. 



Hermaphrodism.— An individual possessing both 

 male and female organs of reproduction, is called a 

 hermaphrodite. Such a combination is very rare among 

 higher animals ; but it is by no means uncommon among 

 plants and the lower forms of animal life. The snail, 

 the oyster, the earthworm, the barnacle, and the com- 

 mon tapeworm are examples of true hermaphrodites. 

 So-called human hermaphrodites are usually individu- 



