402 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



the mutation theory, published a year later, which marked almost 

 as great a transformation in our views of variation and displayed the 

 whole evolution problem in a new light. In the era that followed, 

 the study of heredity quickly became not only an experimental but 

 almost an exact science, fairly comparable to chemistry in its sys- 

 tematic employment of qualitative and quantitative analysis, syn- 

 thesis, prediction, and verification. More and more clearly it be- 

 came evident that the phenomena of heredity are manifestations of 

 definite mechanism in the living body. Microscopical studies on the 

 germ-cells made known an important part of this mechanism and 

 provided us with a simple mechanical explanation of Mendel's law. 

 And suddenly in the midst of all this, by a kaleidoscopic turn, the 

 fundamental problem of organic evolution cr^ystallizes before our 

 eyes into a new form that seems to turn all our previous conceptions 

 topsy-turvy. 



I will comment briefly on this latest view of evolution, partly be- 

 cause of its inherent interest, but also because it again exemplifies, 

 as in the -case of embryology, that temptation to wander off into 

 metaphysics (sit venia verbo) which seems so often to be engendered 

 by new and telling discoveries in science. The fundamental ques- 

 tion which it raises shows an interesting analogy to that encountered 

 in the study of embryology, and may conveniently be approached 

 from this side. 



To judge by its external aspects, individual development, like evo- 

 lution, would seem to proceed from the simple to the complex ; but is 

 this true when we consider its inner or essential nature? The egg 

 appears to the eye far simpler than the adult, yet genetic experiment 

 seems continually to accumulate evidence that for each independent 

 hereditary trait o-f the adult the Q,gg contains a corresponding some- 

 thing (we Imow not what) that grows, divides, and is transmitted by 

 cell division without loss of its specific character and independently 

 of other somethings of like order. Thus arises what I will call the 

 puzzle of the microcosm. Is the appearance of simplicity in the egg 

 illusory? Is the hen's Qgg fundamentallj' as complex as the hen. and 

 is development merely the transformation of one kind of complexity 

 into another? Such is the ultimate question of ontogeny, which in 

 one form or another has been debated b}' embryologists for more than 

 two centuries. We still can not answer it. If we attempt to do so 

 each replies according to the dictates of his individual temperament — 

 that is to say, he resorts to some kind of symbolism — and he still re- 

 mains free to choose that particular form which he finds most con- 

 venient, provided it does not stand in the way of practical efforts to 

 advance our real knowledge through observation and experiment. 

 Those who must have everything reduced to hard and fast formulas 

 v/ill no doubt find this rather disconcerting; but worse is to follow. 



