THE PRESENT OUTLOOK OF VERTEBRATE 



MORPHOLOGY. 1 



I . General. 



TWY. last quarter of a century will ever remain memor- 

 able in the history of animal biology as the period 

 of what may be termed the embryological reaction. At its 

 outset, the field of comparative embryology, first entered by 

 von Baer, followed by Allen Thomson, von Kolliker and 

 Haeckel, under the application of new methods by hundreds 

 ol willing explorers, gave promise of revealing the stages 

 through which the diverse forms of animal structure have 

 been attained, and, correlatively, of enabling us to form at 

 least a sounder conception of the complex inter-relationships 

 of animal forms, and of the characters demanded of the 

 ancestral "LTrthier" and of the lines along which to seek 

 that. During the period, which will always be associated 

 with the names of Balfour, His, Dohrn,the Brothers Hertwig, 

 Van Beneden, Duval, Kowalewsky, Whitman, and Minot, 

 as leaders in the great European countries and America, 

 the conception that ontogeny is generally recapitulatory of 

 phylogeny seemed early destined to prove a reality, and the 

 advancing structural complexities of the organs in the 

 ascending series of animals appeared to be the direct 

 effects of a correspondingly progressive functional differ- 

 entiation of the animal body. As a natural consequence 

 of this, and in accordance with the generally accepted 

 belief that land animals have for the most part had an 

 aquatic origin, and that the fresh- water creatures have 

 mostly been derived from aquatic ancestors, attention 

 became more and more concentrated upon the lower classes 

 of marine invertebrates ; and so violent was the reaction 

 that the department of vertebrate morphology, within which 

 the foundations of the science had been built up, lay at 



1 Apropos of the appearance of Kukenthal's "Vergleichd-anatomische 

 und entwicklungsgeschz Untersuchuniren an Waltieren " {Denkschr. d. 

 Medic- Naturwiss. Gesellsch. Jena, Bd. iii., 1889-1893, 366 pp. and 25 

 plates) and Semon's " Zoologische-Forschungsreisen in Australien und 

 Malayischen Archipel," i. {ibid., Bd. iv., pp. 50, with 8 plates), 1893. 



