228 EARLY STUDIES IN COMPARATIVE ANATOMY 



were persuaded that only microscopic organisms, and 

 perhaps some internal parasites, originated spontaneously. 

 The rooting-out of the theory from these last refuges 

 does not come within the period covered by our history. 



Birds Gizzards'^ 



Redi ridicules jiElian's explanation of the swallowing 

 of stones by the crane, viz. that they serve partly for 

 food and partly for ballast, for the stones, he says truly, 

 are found in birds that never fly. Borelli had investi- 

 gated the matter, and found reasons forv supposing that 

 the stones aid in digestion. He passed glass bulbs into 

 the gullet, and found that they were pulverised in the 

 gizzard. Redi shows that solid glass balls and bullets 

 are scratched ; open bulbs, if they happen to pass 

 through uninjured, are filled with an acid fluid, which 

 he takes to be the secretion of the oesophageal glands. 

 Trituration, he remarks, does not suffice for digestion ; 

 there must be " fermentation " as well. 



Life-history of the Eel'^ 



Redi satisfied himself by personal inquiry that eels 

 visit the sea in autumn, for the purpose, as he supposed, 

 of egg-laying. He had also seen the elvers ascending 

 the rivers in spring. Aristotle had taught that eels lay 

 no eggs, and may perhaps be generated from earth- 

 worms. 



There is much more to tell about Redi, but we must 

 content ourselves with glimpses of his work. 



^ Esp. intomo diversi cosi naturali. 

 2 Os8. intorno agli animali viventi, &c. 





