l] HEREDITY 9 



use of them only can the great resemblance between the individuals 

 grouped together in the same species be accounted for. When, as 

 occasionally happens, members of different 'species are fertile inter 

 se, the offspring is termed a hybrid, and hybrids in the majority of 

 cases are not fertile. 



It has been pointed out, that whereas germs are in most cases 

 exceedingly different from their parents, they never- 



Heredity - . i i i 



and theless in process 01 growth come to resemble them. 



This tendency to reproduce the characters of the 

 parent is called heredity. If the germ undergoes a large part of 

 its development within a hard case, like a chick within the eggshell 

 or in a cavity of the parent's body, it is called an embryo; if it 

 moves freely about, it is termed a larva. 



In the case of the development of an animal which has originated 

 sexually, that is from the coalescence of two germs, the tendency is 

 for it to assume characters intermediate between those of the two 

 parents. Thus it is easy to see how sexual reproduction tends to 

 annul the differences existing between members of the same species, 

 by constantly producing means between them. When therefore a 

 large number of individuals are found with very close resemblances, 

 it is a reasonable supposition that the agent, which has caused this, 

 is sexual reproduction ; in other words, that they constitute a 

 species. It is not however to be assumed that in every case 

 conjugation results in the production of an animal exactly inter- 

 mediate in character between the parents. In a large number of 

 cases where father and mother differ from one another by some 

 well-marked character unconnected with their sex the child resembles 

 closely the father or the mother, a result denoted by the term 

 prepotent applied to the parent which the offspring resembles. 

 When however the children resulting from such a union are mated 

 together, some of the grandchildren resemble one grandparent and 

 some the other grandparent : three-fourths resemble the prepotent 

 grandparent, and the character which they inherit is called the 

 dominant character, and one fourth the other grandparent and 

 the character which reappears in them is called the recessive 

 character. When the grandparents differ in two characters, the 

 same law holds with respect to each character, i.e. three-fourths of 

 the offspring resemble one grandparent and one fourth the other 

 but not all the same children fall into the same group in the case 

 of each character, and so some children inherit the dominant 

 character from one parent and the recessive from another, and thus 



