What is Heredity? 11 



great-grandson of Sappho ; so that, according to the 

 common expression, he had only one-sixteenth of her 

 blood in liis veins. 



Another aspect of onr subject mnst be kept constantly 

 in mind. Among the higlier animals heredity usually 

 manifests itself only by what is known as sexual lepro- 

 duction, — that is, the development of new individuals 

 from fertilized eggs; but in the lower forms of life 

 another kind of reproduction, the development of new 

 individuals by budding or by analogous processes, is even 

 more common. Among the hydroids heredity may mani- 

 fest itself by the formation of new animals, with all the 

 characteristics of the parent, on almost any part of the 

 body of the latter, and in certain plants the smallest 

 fragment of tissue may become a new and perfect plant, 

 capable of producing others in the same way or by seeds. 

 The most sure and rapid way to get new sea-anemones 

 is to tear an old one to pieces. As a rule this power is 

 confined to the lower forms of life, but certain animals 

 which are by no means low or simple in structure multi- 

 ply asexually, and the offspring thus produced inherit, 

 like those developed from eggs, all the characteristics of 

 the jiarent. 



This then is the problem of heredity, certainly one of 

 the grandest secrets of nature. When we reflect upon 

 its obscuritj and complexity we may fairly ask what hope 

 there is of discovering its solution; of reaching its true 

 meaning, its hidden laws and causes. If it is true 

 that, in each egg, all the functions and faculties of a 

 definite mature animal lie hidden, without any corre- 

 sponding organs, must we not regard heredity as a inys- 

 tery too great for solution; as something which must be 

 accepted as it is without scientific explanation? 



Thirty years ago the adaptation of each organ of an 



