112 The Insides and the Wor\ings of Living Things 



variety of modification in order to subserve as great a variety of func- 

 tions; while another structure, such as the eye, is made in different sub- 

 kingdoms on fundamentally different plans, notwithstanding that it has 

 throughout to perform the same function? Will anyone have the hardi- 

 hood to assert that in the case of the skeleton the Deity has endeavored 

 to show his ingenuity, by the manifold functions to which he has made 

 the same structure subservient; while in the case of the eye he has en- 

 deavored to show his resources, by the manifold structures which he has 

 adapted to serve the same function? If so, it becomes a most unfortunate 

 circumstance that, throughout both the vegetable and the animal king- 

 dom, all cases which can be pointed to as showing ingenious adaptation 

 of the same typical structure to the performance of widely different 

 functions — cases of homology without analogy — are cases which come 

 within the limits of the same natural group of plants and animals, and 

 therefore admit of being equally well explained by descent from a com- 

 mon ancestry; while all cases of widely different structures performing 

 the same function — or cases of analogy without homology — are to be 

 found in different groups of plants and animals, and are therefore sug- 

 gestive of independent variations arising in the different lines of heredi- 

 tary descent." 



Blood will Tell 



Everybody knows that " blood will tell," but very few 

 of us seem to be quite clear as to just what it is that it will 

 tell, or how. Most of us have assumed quite uncritically that 

 there is something in the " blood " or hereditary strain that 

 binds together all of a kind. This assumption rests on rather 

 broad human experience and is perfectly sound, although it 

 it not true that hereditary traits are somehow transmitted by 

 the red juice flowing in our veins. While the blood does not 

 carry the characters from generation to generation, we do 

 know that it does bear distinct characteristics in an uncanny 

 parallelism to kinship. These facts have been acquired quite 

 recently, and could not have been known when the saying, 

 ** blood will tell," came into our common consciousness. 



This new knowledge rests upon a rather subtle line of 

 studies developed since the beginning of this century. To 

 understand its implications and its methods, we must go back 



