112 EMBRYOLOGY FROM GALEN [pt. ii 



the parrot, the crow, and so to the fowl. Side by side with a 

 reference to the famous poem of Prudentius {Multi sunt Presbyteri, 

 translated by J. M. Neale) about the steeple-cock, we find an 

 excellent account of the generation of the chick in the c:gg. The book 

 is illustrated sumptuously, but unfortunately there is only one picture 

 of embryological interest, namely, a chick in the act of hatching. 



In Aldrovandus' embryology there is much discussion of Aristotle 

 and Galen, but traces of an independent spirit abound. Pliny's view 

 that the heart was formed in the white is "exploded", and Aldro- 

 vandus says that it is formed on the yolk-membrane. He refutes the 

 opinion of Galen also that the liver is first formed, in connection 

 with which he says, "In order that I might bring to an end this 

 controversy between the philosophers and the physicians I followed 

 with the keenest curiosity and diligence the incubation of 22 hen's 

 eggs, opening one each day; thus I found Aristotle's doctrine to be the 

 truest. And because apart from the fact that these matters are most 

 worthy of being looked into they provide also the greatest pleasure 

 and entertainment I have thought it well to describe them as clearly 

 and briefly as possible". 



Aldrovandus also contradicts Albertus, and propounds a new 

 theory, namely, that the spiritualia (the organs in the thorax) are 

 formed from the seed of the cock {ex maris semine sunt). This seed 

 he aflfirms to be present in the egg, and he identifies it with the 

 chalazae, thus anticipating Fabricius ab Aquapendente, but not 

 going quite so far, and explicitly opposing Gaza, who had said not 

 long before that the chalazae were simply congealed water. Aldro- 

 vandus' admiration for Aristotle is extreme, and, though he differs 

 from him about the chalazae, he defends the Aristotelian opinion 

 that the chick was made from the white but nourished from the yolk. 

 His argument for this is new, however; it is that, during incubation, 

 the latter liquefies but the former hardens; now in all digestion 

 liquefaction takes place, and in all growth hardening, therefore, etc. 

 This argument is a great deal more cogent than most of those which 

 were current between 1550 and 1650. He goes out of his way to 

 castigate Albertus for saying that the yolk moves up into the sharp 

 point of the egg, for experience assures him that it does not, "as I 

 have observed by cutting open an egg after one day's incubation". 

 A striking instance of his powers of observation was his description 

 of the "egg-tooth" of embryonic birds, a discovery made anew in 



