Malpighi.--The observer in embryology who looms into prominence between Harvey and Wolff is Malpighi. He supplied what was greatly needed at the time--an illustrated account of the actual stages in the development of the chick from the end of the first day to hatching, shorn of verbose references and speculations. His observations on development are in two separate memoirs, both sent to the Royal Society in 1672, and published by the Society in Latin, under the titles _De Formatione Pulli in Ovo_ and _De Ovo Incubato_. The two taken together are illustrated by twelve plates containing eighty-six figures, and the twenty-two quarto pages of text are nearly all devoted to descriptions, a marked contrast to the 350 pages of Harvey unprovided with illustrations. His pictures, although not correct in all particulars, represent what he was able to see, and are very remarkable for the age in which they were made, and considering the instruments of observation at his command. They show successive stages from the time the embryo is first outlined, and, taken in their entirety, they cover a wide range of stages. His observations on the development of the heart, comprising twenty figures, are the most complete. He clearly illustrates the aortic arches, those transitory structures of such great interest as showing a phase in ancestral history. [Illustration: Fig. 61.--Selected Sketches from Malpighi's Works. Showing Stages in the Development of the Chick (1672).] He was also the first to show by pictures the formation of the head-fold and the neural groove, as well as the brain-vesicles and eye-pockets. His delineation of heart, brain, and eye-vesicles are far ahead of those illustrating Wolff's _Theoria Generationis_, made nearly a hundred years later. Fig. 61 shows a few selected sketches from the various plates of his embryological treatises, to compare with those of Wolff. (See Fig. 63.) [Illustration: Fig. 62.--Marcello Malpighi, 1628-1694.] The original drawings for _De Ovo Incubato_, still in possession of the Royal Society, are made in pencil and red chalk, and an examination of them shows that they far surpass the reproductions in finish and accuracy. While Harvey taught the gradual formation of parts, Malpighi, from his own observations, supposed the rudiments of the embryo to pre-exist within 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.