102 PERIOD IV. 



Baer and the Development of Animals. 



The curiosity of the ancient Greeks led them to look 

 for the chick within the egg, and Aristotle mentions 

 the beating of the heart as a thing which might be 

 observed in a third-day embryo. After the revival of 

 science Fabricius of Acquapendente figured the chief 

 stages of development, from the first visible rudiments 

 to the escape from the egg-shell. Harvey, the dis- 

 coverer of the circulation, not only studied the develop- 

 ing chick, but took advantage of the rare opportunity 

 of dissecting breeding does from the royal parks. His 

 treatise on Generation is unfortunately impaired by 

 Aristotelian philosophy, and some of the theories there 

 set forth gave much trouble to Swammerdam. The 

 oft-cited maxim " Omne vivum ex ovo " does not occur 

 exactly in this form in Harvey's writings, 1 nor does it 

 fairly state his own belief. Those who read his De 

 Generations will see that his knowledge was insufficient 

 to justify so wide a generalisation ; on this head it is 

 enough to mention that he was persuaded of the pro- 

 duction of insects without parents from putrefying 

 matter. 9 



Malpighi was the first to apply the microscope to 

 the embryonic chick. His figures are surprisingly full 



1 Linnaeus (Fund. Bot. 134, and Sponsalia Plantarum) gives 

 it as above; Harvey has "Ex ovo omnia"; "ovum esse primor- 

 dium commune omnibus animalibus," etc. 



a Harvey need not have gone outside the writings of Aristotle 

 to get the substance cf his generalisation. He would have found 

 there that the chief task of both plants and animals is propaga- 

 tion, either by seeds, or eggs, which Aristotle believed to be 

 equivalent to seeds (Hist, anim., VIII., i.; De anim. gen., I., iv. ; 

 I., xxiii.). Aristotle excepted the "imperfect animals," such as 

 insects, and the seedless plants, concerning both of which his 

 knowledge was misty and inaccurate ; there is no indication that 

 Harvey was better informed. 



