ZOOLOGY 445 



eighteenth century, contended that the germ was a minute replica of 

 the adult which formed it, a multum in parvo which simply unfolded 

 and enlarged to produce another adult organism; Wolff, however, 

 showed that this view lacked a basis in fact, and that as we now 

 universally believe, embryonic history is a true development from the 

 simple and unorganized to the progressively more and more specialized 

 later conditions — that it is, in a word, an epigenesis. The great name 

 of the infancy of embryology is that of Von Baer (1792-1876). This 

 acute observer and thinker was struck by the similarity of early stages 

 in the development of quite different adult animals. Birds and rep- 

 tiles and even mammals pass through stages when they possess gill-slits 

 like those of fishes, related to heart and blood-vessels like the similar 

 structures in lower vertebrates; butterflies and flies and beetles are 

 somewhat alike in their larval stages, when as caterpillars and maggots 

 and grubs they not only resemble one another remarkably but they are 

 also very like worms. Under the influence of the evolution doctrine, 

 then becoming more generally accepted, Von Baer and a host of fol- 

 lowers extended the science of comparative embryology until Haeckel 

 in 1866 ventured to state the " Law of Recapitulation," or the " Bio- 

 genetic Law," in the following rigid terms : Ontogeny recapitulates 

 phylogeny. (The development of an individual reviews the past his- 

 tory of its species.) Led by their enthusiasm many of the later nine- 

 teenth century zoologists followed too implicitly the lines of the 

 embryonic record, though Haeckel himself, the most radical advocate 

 of the law, pointed out that there are many serious omissions in the 

 narrative, that false passages are inserted as the result of purely larval 

 and embryonic needs and adaptations, while many alterations in the 

 way of anachronisms have been made. Of late years there has been a 

 strong reaction from the complete acceptance of the principle as a 

 reliable mode of interpreting embryonic histories. But I believe 

 zoologists generally feel that used with due caution the law has a high 

 value for the student of evolution, and they realize that embryology 

 is perhaps more significant in other respects than in showing exactly 

 how in past times any given species has evolved. The present tasks in 

 this department, now so thoroughly investigated, are to distinguish 

 between the false and the true portions of the record, between the new 

 and the old, and to ascertain the physiology of development, in order 

 to gain a more complete knowledge of racial history and of the dynamics 

 of organic nature. 



The study of the fossil remains of animal organisms, or paleon- 

 tology, is the fourth division of structural zoology, which as an inde- 

 pendent branch dates back to the time of Cuvier, scarcely a hundred 

 years ago. Vestiges of creation were indeed known long before that 

 time, but they were variously regarded as freaks of geological forma- 



