INTRODUCTION. 157 



to be known : as that proceeds from the imitation of types or 

 forms, so this proceeds from the knowledge of natural things. 

 Each has its origin in sense and experience, and it is impos- 

 sible that there can rightly be either art or science without 

 visible instance or example. In both, that which we perceive 

 in sensible objects differs from the image itself which we retain 

 in our imagination or memory. That is the type, idea, forma 

 informans ; this is the imitation, the Eidos, the abstract species. 

 That is a thing natural, a real entity ; this a representation or 

 similitude, and a thing of the reason. That is occupied with 

 the individual thing, and itself is single and particular ; this is 

 a certain universal and common thing. That in the artist and 

 man of science is a sensible thing, clearer, more perfect ; this a 

 matter of reason and more obscure : for things perceived by 

 sense are more assured and manifest than matters inferred by 

 reason, inasmuch as the latter proceed from and are illustrated 

 by the former. Finally, sensible things are of themselves and 

 antecedent ; things of intellect, however, are consequent, and 

 arise from the former, and, indeed, we can in no way attain to 

 them without the help of the others. And hence it is, that 

 without the due admonition of the senses, without frequent ob- 

 servation and reiterated experiment, our mind goes astray after 

 phantoms and appearances. Diligent observation is therefore 

 requisite in every science, and the senses are frequently to be 

 appealed to. We are, I say, to strive after personal experience, 

 not to rely on the experience of others ; without which, indeed, 

 no one can properly become a student of any branch of natural 

 science, nor show himself a competent judge of what I am 

 about to say on the subject of generation ; for without expe- 

 rience and skill in anatomy, he would not better understand 

 me than could one born blind appreciate the nature and dif- 

 ference of colours, or one deaf from birth judge of sounds. I 

 would, therefore, have you, gentle reader, to take nothing on 

 trust from me concerning the generation of animals ; I appeal 



