Page:Popular Science Monthly Volume 67.djvu/106

100 Harvey, little of substantial value had been produced. The earliest attempts were vague and uncritical, and, naturally, embraced only fragmentary views of the more obvious features of body formation. Nor, indeed, are we to look for much advance in the field of embryology even in Harvey's time. The reason for this will be obvious when we remember that the renewal of independent observation had just been brought about in the preceding century, when, in 1543, the science of anatomy had been reformed by Vesalius.

Harvey himself was one of the pioneers in the intellectual awakening. By his immortal discovery of circulation of the blood (1619-1628) he had established a new physiology. Now, studies on the development of the body are more special, they involve observations on minute structures and recondite processes, and must, therefore, depend upon considerable advances in anatomy and physiology. Naturally the science of embryology came later.

Harvey.—Harvey's was the first attempt to make a critical analysis of the process of development, and that he did not attain more was not due to limitations of his powers of discernment, but to the necessity of building on the general level of the science of his time, and, further, to his lack of instruments of observation and technique. Nevertheless, Harvey may be considered as having made the first independent advance in embryology.

By clearly teaching, on the basis of his own observations, the gradual formation of the body by aggregation of its parts, he anticipated Wolff. This doctrine came to be known under the title of 'epigenesis,' but Harvey's epigenesis was not, as Wolff's was, directed against a theory of predelineation of the parts of the embryo, but against the ideas of the medical men of the time regarding the metamorphosis of germinal elements. It lacked, therefore, the dramatic setting which surrounded the work of Wolff in the next century. Had the doctrine of preformation been current in Harvey's time, we are quite justified in assuming that he would have assailed it as vigorously as Wolff did.

Harvey's embryological work was published in 1651 under the title 'Exercitationes de Generatione Animalium.' It embraces not only observations on the development of the chick, but also on the deer and some other mammals. He being the court physician of Charles I., that sovereign had many deer killed in the park, at intervals, in order to give Harvey the opportunity to study their development.

As fruits of his observation on the chick, he showed the position in which the embryo arises within the egg. viz., in the white opaque