XVI THE HISTORY OF ZOOLOGY 671 



still associated. He was also the first to study the de^relopment 

 of the Chick under the microscope, and was one of the earliest 

 supporters of the .theory oi pre-formation,'^ according to which all 

 the parts and organs of the adult are present in the germ, so that 

 there is no differentiation, but only an unfolding. Leeuwenhoek 

 discovered blood-corpuscles, striated muscle-fibres, dentinal canals, 

 and epiderm-cells, observed the circulation of the blood in the 

 tadpole's tail, and described many of the lesser forms of life, such 

 as Infusoria, Rotifers, and Hydra. Swammerdam investigated the 

 anatomy of Insects and ■ Molluscs, and the metamorphosis of 

 Insects, and described the three " sexefe " of Bees. The researches 

 of Hook and Grew were mainly botanical ; both they and Malpighi 

 discovered in the tissues of plants little spaces with firm walls and 

 full of fluid ; these they called cells, thus taking the first step in 

 the structural analysis of the higher organisms. 



Another discovery of fundamental importance was made in 1677 

 when Louis de Hamen observed and described the sperms of 

 animals. These were at first thought to be the young, which only 

 required to be nourished in the egg to grow into the embryo or 

 fcetus, and were therefore considered to disprove the theory of 

 the ovulists — such as Harvey, who made the egg the origin of the 

 new generation — in favour of that of the spermatists, who believed 

 the whole material to be furnished by the male parent. 



Belonging also to this period are Redi's experiments on genera- 

 tion, in which he begata the work of establishing the doctrine of 

 biogenesis, according to which organisms originate only from pre- 

 existing organisms, and of demolishing that of ahiogenesis, or 

 "spontaneous generation," which, maintained from the time of 

 Aristotle onwards, held that Flies, Lice, Worms, and other animals 

 were directly generated in mud, putrefying flesh, dung, &c., having, 

 therefore, no living progenitors. Eedi's contribution to this 

 question lay in proving, for the first time, that the maggots, " bred " 

 in putrefying meat, were the products of eggs laid thereon by 

 Flies. 



Thus the seventeenth century saw a great advance in the 

 knowledge of animal structure and function, and the way was 

 paved towards a rational classification. As we have already seen, 

 Ray, towards the end of the century, gave zoology as a whole a 

 scientific form ; he first grasped the ideas of species and of specific 

 characters, acknowledged anatomy as the basis of classification, 

 and introduced a greatly increased precision in the definition of 

 species and other groups, and in terminology. He had, however, 

 no clear idea of genera, his genera being rather what we now call 

 orders or families, and he showed an undue conservatism in 



1 Often known as the theory of evolution. As, however, the latter word ia 

 now universally used in a different sense, it is advisable to drop it in this 

 connection, and to employ the synonym pre-formatimi. 



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