132 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



appropriate stimulus has been received, into the completed embryo 

 by the actions and reactions of its own constituents on the one hand 

 and the influence of the fitting factors of the environment upon the 

 other. Digby has not received his due in the past; he stands to 

 embryology as an exact science, much in the same relationship as 

 Bacon to science as a whole. 



"Generation is not made", he says, "by aggregation of like parts 

 to presupposed like ones; nor by a specificall worker within; but by 

 the compounding of a seminary matter with the juice which accrueth 

 to it from without and with the steams of circumstant bodies, which 

 by an ordinary course of nature are regularly imbibed in it by degrees 

 and which at every degree doe change it into a different thing ..." (see 

 p. 317). "Therefore to satisfie ourselves herein, it were well we made 

 our remarks on some creatures that might be continually in our power 

 to observe in them the course of nature every day and hour. Sir lohn 

 Heydon, the Lieutenant of his Majesties Ordnance (that generous 

 and knowing Gentleman, and consummate Souldier both in theory 

 and practice) was the first that instructed me how to do this, by 

 means of a furnace so made as to imitate the warmth of a sitting hen. 

 In which you may lay severall eggs to hatch, and by breaking them 

 at severall ages you may distinctly observe every hourly mutation 

 in them if you please." Sir Kenelm then goes on to describe the 

 events that take place in the incubating egg, which he does very 

 accurately, though briefly. In vivipara, he says, the like experiments 

 have been made, and the like conclusions come to by "that learned 

 and exact searcher into nature. Doctor Harvey" — these he must 

 have learnt of by word of mouth, for Harvey's book had not at that 

 time been published. As regards heredity, he adopts a pure theory 

 of pangenesis, and has more to say about it than any other writer 

 of his time. He is sure that the heart is first formed both in ovipara 

 and vivipara, "whose motion and manner of working evidently ap- 

 pears in the twinckling of the first red spot (which is the first change) 

 in the egge". 



Sir Kenelm Digby not only anticipated the outlook of the physico- 

 chemical embryologist, but he also foreshadowed with considerable 

 accuracy Wilhelm Roux's definition of interim embryological laws. 

 "Out of our short survey", he says, "of which (anserable to our weak 

 talents, and slender experience) I perswade myselfe it appeareth 

 evidently enough that to effect this worke of generation there needeth 



