HEREDITY. 239 



While, however, the general truth that organisms of a 

 given type uniformly descend from organisms of the same 

 type, is so well established by infinite illustrations, as to have 

 assumed the character of an axiom ; it is not universally 

 admitted that non-typical peculiarities are inherited. While 

 the botanist would be so incredulous if told that a plant oi 

 one class had produced a plant of another class, or that from 

 seeds belonging to one order individuals belonging to another 

 order had grown, that he would deem it needless to examine 

 the evidence ; and while the zoologist would treat with con- 

 tempt the assertion, that from the egg of a fish a reptile had 

 arisen, or that an implacental mammal had borne a pla- 

 cental mammal, or that an unguiculate quadruped had sprung 

 from an ungulate quadruped, or even that from individuals 

 of one species offspring of an allied species had proceeded ; 

 yet there are botanists and zoologists who do not consider it 

 certain, that the minor specialities of organization are trans- 

 mitted from one generation to another. Some naturalists 

 seem to entertain a vague belief, that the law of Heredity 

 applies only to main characters of structure, and not to de- 

 tails ; or, at any rate, that though it applies to such details 

 as constitute differences of species, it does not apply to 

 smaller details. The circumstance that the tendency to re- 

 petition, is in a slight degree qualified by the tendency to 

 variation (which, as we shall hereafter see, is but an indirect 

 result of the tendency to repetition), leads some to doubt 

 whether Heredity is unlimited. A careful weighing of the 

 evidence, however, and a due allowance for the influences by 

 which the minuter manifestations of Heredity are obscured 



V 



will remove the grounds for this scepticism. 



First in order of importance, comes the fact, that not only 

 are there uniformly transmitted from an organism to its 

 offspring, those traits of structure which distinguish the class, 

 order, genus, and species ; but also those which distinguish 

 the variety. We have numerous cases, among both plants 

 and animals, where, by natural or artificial conditions, there 



