THE SHAPES AND SIZES OF ANIMALS 157 



those which are larger also when adult. It is 

 true that an ostrich lays a bigger egg than a hen, 

 and a hen than a sparrow; but it is very easy 

 to show that the relation is not a general one, 

 and that size at birth has no necessary relation 

 to size in the adult condition. For example, 

 a crayfish and a lobster are two closely allied 

 animals, and yet the crayfish lays the larger egg 

 of the two, though the adult is not more than 

 a quarter the length of a lobster. Or again, were 

 Spencer's contention right, then an eight months' 

 child, being born of smaller size than the average, 

 should not attain to average stature. It is more 

 probable that the real explanation is a much more 

 complicated one, and that there is for each animal 

 a certain average size which is most advantageous 

 to the animal when living wild in its natural 

 condition. Natural Selection will then tend to 

 preserve this average size by placing at a dis- 

 advantage those individuals which depart from it 

 conspicuously, whether in the way of excess or 

 diminution. 



In connection with this point, reference must be 

 made to Mr. Galton's law of Regression, enunciated 

 in his recently published and most important book 

 on Natural Inheritance. It is impossible to discuss 

 the subject further on the present occasion, and I 

 will conclude by giving the Law in Mr. Galton's 

 own words, referring my readers for further details 

 to his most fascinating and suggestive work. " If 

 the word ' peculiarity ' be used to signify the 

 difference between the amount of any faculty 



