24 Heredity. 



Still more opposed to the hypothesis of evolution is. 

 the remarkable fact that the changes which take place 

 in the developing egg are not such as would lead directly 

 to the formation of the adult animal. In most cases 

 a circuitous or indirect path is followed, and this in- 

 direct path leads at first towards the adult form of lower 

 members of the group. 



This, the most suggestive fact of modern embryology, 

 may perhaps be made clearer by an illustration. 



Let us try to compare the growth of an egg into an 

 adult animal with the growth of some manufactured 

 product in the hands of its maker. 



The evolutionist view of the development of an or- 

 ganism may be illustrated by the manufacture of a yarn 

 base-ball. A boy, wishing to make a yarn ball, procures, 

 if possible, a small rubber ball, and winds his yarn onto 

 this until the desired size is reached, the only changes 

 during the growth of the ball being the change of size 

 and of material. 



The observed facts of embryology show that the 

 development of an embryo does not take place in any 

 such way as this. It may, however, be illustrated by the 

 growth of a steam-ship in the hands of the builder, who . 

 first lays down an indefinite skeleton, and outlines in a 

 vague way the more prominent features, before any of 

 the details are finished. In order to make the illustration 

 perfect, however, we must imagine the builder to com- 

 mence work upon his steam-ship by laying out the skeleton 

 of a big triareme; we must imagine him to carry this some 

 stages towards completion, and to put into it certain 

 contrivances, such as rowers' benches, which are of no 

 use in a steam-ship. We must imagine that he then 

 abandons his plan, tears down his benches, and uses the 

 material to make a deck; that he changes the shape and 



