LECTURE LXXX. 



INFLUENCE OF LAW OF CORRELATION. 



By the law of heredity and other influences we have dis- 

 covered that when two animals of extreme diversity of type 

 are mated the offspring does not, as a general rule, have the 

 peculiar or extreme characters of either parent developed 

 as fully as either parent. They seem, in a sense, to blend 

 together and form a happy medium. This same thing is illus- 

 trated in photography. By the continuous focusing of a 

 camera on a number of different animals, using the same 

 plate all the time, and then developing the same, we will 

 discover that if there were certain characteristics in common 

 in all of the animals these will be very marked in the photo. 

 On the other hand, if every other animal is of a different 

 type to what the preceding one was we will have nothing 

 but a blur. 



In the same connection where animals which have some 

 points in common and in other respects are widely different 

 are mated the offspring will show prominence of those char- 

 acters which are in common and the suppression of those 

 which are different in the parents. 



In the arrangement of these dominant characters in the 

 organization there seems to be a principle of development and 

 suppression, which is designated by naturalists as the law 

 of correlation. The law may be denned in a simple term 

 as follows: Any peculiarity in the development of one organ 

 or set of organs is usually accompanied by a corresponding 

 modification or suppression of organs belonging to some 

 other part of the body. 



This law seems to be in keeping with nature, that is, that 

 each and every part should be properly developed. If by 

 artificial means, or by selection, we seek to develop one par- 

 ticular part, that in time the same will be checked as other 

 necessary parts will not be developed in a sufficient degree 

 to sustain life. 



In blind people where the sense of sight is lacking some 



