172 THE GROWTH OF SCIENCE IN THE NINETEENTH CENTURY. 



as a tiny ball, of which we can, even acknowledging to the full the 

 limits of the optical analysis at our command, assert with confidence 

 that in structure, using that word in its ordinary sense, it is in all cases 

 absolutelj^ simple. It is equally well known that the features of form 

 which supply the characters of a grown-up living being, all the manj'^ 

 and varied features of even the most complex organism, are reached 

 as the goal of a road, at times a long road, of successive changes: that 

 the life of every being, from the ovum to its full estate, is a serii^s of 

 shifting scenes, which come and go, sometimes changing al)ruptly, 

 sometimes melting the one into the other, like dissolving views, all so 

 ordained that often the final shape with which the creature seems to 

 begin, or is said to begin, its life in the world is the outcome of many 

 shapes, clothed with which it in turn has lived many li\'os ])efore its 

 seeming birth. 



All or nearly all the exact knowledge of the laliored way in which 

 each living creature puts on its proper shape and structure is the 

 heritage of the present century. Although the way in which the chick 

 is molded in the egg was not wholly unknown even to the ancients, 

 and in later years had been told, first in the sixteenth century by 

 Fabricius, then in the seventeenth century in a more clear and striking 

 mannei' by the great Italian naturalist, Malpighi, the teaching thus 

 ofi'ered had been neglected or misinterpreted. At the close of the 

 eighteenth century the dominant vicAv was that in the making of a crea- 

 ture out of the egg there was no putting on of wholly new parts, no 

 epigenesis. It was taught that the entire creature lay hidden in the 

 egg^ hidden by reason of the very transparency of its substance, lay 

 ready-made, but folded up, as it were, and that the process of develop- 

 ment within the egg or within the womb was a mere' unfolding, a 

 simple evolution. Nor did men shrink from accc^pting the logical out- 

 come of such a view — namely, that within the unborn creature itself 

 la}" in like manner, hidden and folded up, its ofl'spring also, and within 

 that again its offspring in turn, after the fashion of a cluster of ivory 

 balls carved by Chinese hands, one within the other. This was no 

 fantastic view put forward by an imaginative dreamer; it was seri- 

 ously held by sober men, even by men like the illustrious Haller, in 

 spite of their recognizing that as the chick grew in the egg some 

 changes of form took place. Though so early as the middle of the 

 eighteenth century Friedrich Casper Wolfi' and, later on, others had 

 strenuously opposed such a view, it held its own not only to the close 

 of the century, but far on into the next. It was not until a quarter 

 of the present century had been added to the past that Von Baer made 

 known the results of researches which once and for all swept away the 

 old view. He and others working after him made it clear that each 

 individual puts on its final form and structure not ])y an unfolding of 

 preexisting hidden features, but ])y the formation of new parts through 



