INTRODUCTION. 3 



ceeded, was the cicatricula. This Fabricius had looked upon 

 as a blemish, a scar left by a broken peduncle. In his 

 Anatomical Exercises on the Generation of Animals (1651), 

 Harvey describes the little cicatricula as expanding under 

 the influence of incubation into a wider structure, which 

 he calls the eye of the egg ; and at the same time sepa- 

 rating into a colliquamentum. In this colliquamentum, 

 according to him, there appears, as the first rudiment of 

 the embryo, the heart or punctum saliens, together with 

 the blood-vessels. These gradually gather round them 

 the solid parts of the body of the chick. Harvey clearly 

 was of opinion that the embryo arose, by the successive 

 formation of parts, out of the homogeneous nearly liquid 

 colliquamentum. He was an early advocate of the doctrine 

 of epigenesis. 



Notwithstanding the weight of Harvey's authority, the 

 doctrine of epigenesis subsequently gave way to that of 

 evolution, according to which the embryo pre-existed, even 

 though invisible, in the ovum, and the changes which took 

 place during incubation consisted not in a formation of 

 parts, but in a growth, i. e. in an expansion with concomitant 

 changes, of the already existing germ. Of this theory 

 Malpighi is frequently said to have been the founder. In 

 a limited sense this is true. In his letter to the Royal 

 Society of London, De Formatione Pulli in Ovo (1672), he 



:onfesses himself compelled to admit that even in unincu- 

 bated eggs an embryo was present (Quare pulli stamina in 

 ovo pre-existere, altioremque originem nacta esse fateri 

 convenit). Yet he evidently struggled against such a con- 

 clusion, and instead of developing a consistent theory of 



evolution, left the earliest stages of the embryo as too 

 mysterious to be profitable objects of study, and contented 

 himself with tracing out the events of later days. From his 

 descriptions it is clear that his so-called unincubated eggs 



12 



