342 THE POPULAR SCIENCE MONTHLY. 



years ago, not only were we devoid of any accurate knowledge of the 

 mode of development of many groups of animals and plants, but the 

 methods of investigation were rude and imperfect. At the present 

 time there is no important group of organic beings the development 

 of which has not been carefully studied, and the modern methods of 

 hardening and section-making enable the embryologist to determine 

 the nature of the process in each case, with a degree of minuteness 

 and accuracy which is truly astonishing to those whose memories carry 

 them back to the beginnings of modern histology. And the results of 

 these embryological investigations are in complete harmony with the 

 requirements of the doctrine of evolution. The first beginnings of all 

 the higher forms of animal life are similar, and, however diverse their 

 adult conditions, they start from a common foundation. Moreover, 

 the process of development of the animal or the plant from its primary 

 egg or germ is a true process of evolution a progress from almost 

 formless to more or less highly organized matter, in virtue of the 

 properties inherent in that matter. 



To those who are familiar with the process of development all a 

 priori objections to the doctrine of biological evolution appear child- 

 ish. Any one who has watched the gradual formation of a complicated 

 animal from the protoplasmic mass which constitutes the essential 

 element of a frog's or a hen's egg has had under his eyes sufficient 

 evidence that a similar evolution of the animal world from the like 

 foundation is, at any rate, possible. 



Yet another product of investigation has largely contributed to the 

 removal of the objections to the doctrine of evolution current in 1859. 

 It is the proof afforded by successive discoveries that Mr. Darwin did 

 not over-estimate the imperfection of the geological record. No more 

 striking illustration of this is needed than a comparison of our knowl- 

 edge of the mammalian fauna of the Tertiary epoch in 1859 with its 

 present condition. M. Gaudry's researches on the fossils of Pikermi 

 were published in 1868, those of Messrs. Leidy, Marsh, and Cope on 

 the fossils of the Western Territories of America have appeared almost 

 wholly since 1870 ; those of M. Filhol, on the phosphorites of Quercy, 

 in 18T8. The general effect of these investigations has been to intro- 

 duce us to a multitude of extinct animals, the existence of which was 

 previously hardly suspected ; just as if zoologists were to become ac- 

 quainted with a country, hitherto xinknown, as rich in novel forms of 

 life as Brazil or South Africa once was to Europeans. Indeed, the 

 fossil fauna of the Western Territories of America bids fair to exceed 

 in interest and importance all other known Tertiary deposits put to- 

 gether ; and yet, with the exception of the case of the American ter- 

 tiaries, these investigations have extended over very limited areas, 

 and at Pikermi were confined to an extremely small space. 



Such appear to me to be the chief events in the history of the 

 progress of knowledge, during the last twenty years, which account 



