THE EVIDENCE FROM DEVELOPMENT. 183 



lies next to hand in treating of development and the lessons it is 

 calculated to teach. Let us, in the first place, try to discover the 

 place and import of Harvey's teachings concerning development, as 

 compared with those of succeeding investigators and theories. There 

 can be no question that the researches of the nineteenth century 

 have but confirmed and enlarged the observations of Harvey in the 

 seventeenth. " Epigenesis " is seen to be the method of nature in 

 developing the animal form with that " admirable and incomprehen- 

 sible artifice " which Harvey so justly admired. From the primitive 

 and undifferentiated protoplasm of the egg, modern embryology 

 beholds the formation of the chick in a fashion strictly corresponding 

 in all essential details to that outlined by the genius of Harvey. 

 Compared with the views of Malpighi holding. that the egg contained 

 a miniature chick, and that development was merely an unfolding or 

 expansion of already formed parts Harvey's description and theory 

 of development stand forth in marked contrast in respect of their 

 thorough correspondence with the fruits of modern research. Bonnet's 

 theory of the " evolution," through the supply of nutrition, of an 

 already formed chick contained in the egg r meets a like fate to the 

 opinion of Malpighi ; whilst his doctrine of: " emboitement " credit- 

 ing each germ with being the repository of all; future germs when 

 taken literally, shares a like fate with his ideas regarding the evolution 

 of the single animal form. As supplementing the ideas of Harvey 

 by direct observation, we note the philosophic nature of the views of 

 Wolff, through whose researches the foundations of modern embryology 

 may be regarded as having been laid. The line of research leading 

 from Wolff and Pander to the present day may be held to represent 

 merely the direct continuation of the " Exercitations " of Harvey, 

 whose " philosophising " has thus led to results of which its sage 

 founder, with all his perspicuity, could have had no warning or idea. 



The details of the studies in development outlined in this chapter 

 must now be briefly summed up ; whilst a glance at their bearings upon 

 and teachings regarding evolution may form a fitting conclusion to the 

 present stage of our studies. Firstly, then, it is noteworthy that the 

 germ or ovum of all animals excepting the very lowest, or Protozoa 

 appears as a protoplasmic mass, which exhibits all the characters of 

 the microscopic body known as a " cell" (Figs. 87, 89, 92). In the 

 lowest animals just named, the difficulty of distinguishing their germs, 

 and indeed their entire developmental history, arises in great part 

 from their ill-defined nature, and from the marvellous analogies and 

 likenesses they present to their lower plant-neighbours. In the 

 " biological no-man's-land " where the lowest animals and lowest 

 plants meet in a confusing identity of form and function, distinctness 

 of germ-elements may neither be expected nor found. But it is at 

 the same time noteworthy that even in this lowest group of the 



