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 mentioned 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.[1]
On the whole, Malpighi should rank above Harvey as an embryologist, on account of his discoveries and fuller representation, by drawings 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 publications 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.
