34 PERIOD II. 



focus, and to provide each with a separate lens. With 

 such microscopes he managed to study and figure very 

 minute objects, such as blood-corpuscles, spermatozoa, 

 and bacteria. The spermatozoa were brought under 

 his notice by a young Dutch physician named Hamm ; 

 but it was Leeuwenhoek's account of them, and his 

 daring theory of their physiological role, which gave 

 them such celebrity. To Leeuwenhoek we owe the first 

 discovery of the rotifers, the infusoria, Hydra, the 

 yeast-cell, the bacteria, and the generation of aphids 

 without male parents. 



The tradition of the minute anatomists has never been 

 lost, though we shall be unable to pursue it in these pages. 

 Lyonet (see p. 61) even surpassed Swammerdam in the 

 elaborate finish of some of his insect-dissections. 



Early Notions about the Nature of Fossils. 



Throughout the sixteenth century naturalists held 

 animated debates about the shells which are found far 

 from the sea, and even on the top of high hills. Had 

 they ever formed part of living animals or not? Such 

 a question could hardly have been seriously discussed 

 among simple-minded people ; but the learned men of 

 the sixteenth century were rarely simple-minded. They 

 had been trained to argue, and argument could make it 

 plausible that such shapes as these were generated by 

 fermentation or by the influence of the stars. So 

 prevalent were these doctrines that it entitles any 

 early philosopher to the respect of later generations 

 that he should have taken shells, bcnes, and teeth to 

 be evidences of animal life. In this singular roll of 

 honour we find the names of Cesalpini, Palissy, Scilla, 

 Stenson, Hooke, and Woodward. 



In England the struggle between philosophy and 



