io6 POPULAR SCIENCE MONTHLY. 



preexist in the egg. He thought that, possibly, the blood vessels were 

 in the form of tubes, closely wrapped together, which by becoming 

 filled with blood were distended. Nevertheless, in the treatises men- 

 tioned above he is very temperate in his expressions on the whole 

 matter, and evidently believed in the new formation of many parts. 

 In the work published after his death he appears to have been less 

 circumspect. 



Malpighi's work, with that of some of his contemporaries, marks 

 the beginning of the theory of preformation.* 



On the whole, Malpighi should rank above Harvey as an embryol- 

 ogist, on account of his discoveries and fuller representation, by draw- 

 ings and descriptions, of the process of development. As Sir Michael 

 Foster has said : " The first adequate description of the long series of 

 changes, by which, as they melt the one into the other, like dissolving 

 views, the little white opaque spot in the egg is transformed into the 

 feathered, living, active bird, was given by Malpighi. And where he 

 left it, so for the most part the matter remained until even the present 

 century. For this reason we may speak of him as the founder of 

 embryology." 



The Period of Wolff. 



Between Harvey and Wolff, embryology had become dominated by 

 the theory that the embryo exists already preformed within the egg, 

 and, as a result of the rise of this new doctrine, the publications of 

 Wolff had a different setting from that of any of his predecessors. It 

 is only fair to say that to this circumstance is owing, in large part, the 

 prominence of his name in connection with the theory of epigenesis. 

 As we have already seen, Harvey, more than a century before the publi- 

 cations of Wolff, had clearly taught that development was a process 

 of gradual becoming. Nevertheless, Wolff's work as opposed to the 

 new theory was very important. 



While the facts fail to support the contention that he was the 

 founder of epigenesis, it is to be remembered that he has claims in 

 other directions to rank as the foremost student of embryology prior 

 to Von Baer. 



As a preliminary to discussing Wolff's position we should bring 

 under consideration the doctrine of preformation and encasement. 



Rise of the Theory of Predelineation. — The idea of preformation 

 in its first form is easily set forth. Just as when we examine a seed, 

 we find within an embryo plantlet, so it was supposed that the various 

 forms of animal life existed in miniature within the egg. The process, 

 of development was supposed to consist of the expansion or unfolding 

 of this preformed embryo. The process was commonly illustrated by 

 reference to flower buds. " Just as already in a small bud all the 



* See further under the period of Wolff. 



