GENERATION OF ANIMALS 



modern times until the seventeenth century," and 

 his knowledge of the hectocotA^lization of one of the 

 tentacles in the Octopus ; the problem involved in 

 the latter case has not yet been solved. Other 

 problems raised by him have found their solution 

 only in very recent years ; among them may be 

 mentioned the breeding of eels and the anatomy of 

 the hyena.'' His discussion of the reproduction of 

 bees is a remarkable piece of analysis ; and here, 

 again the facts are not yet fully ascertained. It is in 

 connexion with this problem that Aristotle makes his 

 well-known dictum : " But the facts have not yetv 

 been sufficiently ascertained ; and if at any future 

 time they are ascertained, then credence must be 

 given to the direct evidence of the senses rather than 

 to theories — and to theories too provided that the 

 results which they show agree with what is observed." 

 This, indeed, is the principle upon which his work 

 is based : and although he is often forced to rely 

 upon bare theories, it is only because he was unable 

 to obtain experimental data — most insects, he regret- 

 fully remarks, are too small to be observed — in other 

 words, it is only because he lacked the necessary 

 apparatus. For his magnificent apologia (if such it 

 can be called — protreptic would be a better word) on 

 the subject of the study of natural history, the reader 

 should refer to the passage in the first Book of the 

 De partibus (ch. 5). Nevertheless it is probable that 

 his theories, though they sometimes led him astray, 

 did in fact often help him to adopt a correct general 

 outlook, even if the detailed working out of them is 



" By Nicolaus Steno (1638-1686): although the facts were 

 not widely known until the work of J. Miiller in the 19th 

 century (see 754 b 33, n.). "" See p. 565. 



ix 



