August 26, 1898.] 



SGIENGE. 



243 



series ; the thorough and, so far as possible, 

 exhaustive study of the complex and double 

 salts and, fiuallj-, the determination of the 

 atomic masses of the elements with all the 

 precision of which the subject admits, and 

 in the spirit of Stas, of Richards and of 

 Morley. 



WOLCOTT GiBBS. 



A SALF-GENTURY OF EVOLUTION, WITH 



SPECIAL REFERENCE TO THE EFFECTS 



OF GEOLOGICAL CHANGES ON 



ANIMAL LIFE* 



Only a little less than fifty years have 

 passed since the publication of Darwin's 

 Origin of Species, and the general accept- 

 ance by naturalists of the theory of 

 descent. Since 1848 the sciences of embry- 

 ology, cytology and comparative anatomy 

 based on embryology, or, as it is now called, 

 morphology, have been placed on a firm 

 foundation. It is but little over half a cen- 

 tury since the nniformitarian views of Lyell 

 were promulgated. The cell doctrine was 

 born in 1839; the view that protoplasm 

 forms the basis of life was generally received 

 forty years since ; fifty years ago the doc- 

 trine of the conservation of forces was 

 worked out, and already by this time had 

 the idea of the unity of nature dominated 

 the world of science. 



On the fiftieth anniversary, therefore, of 

 our Association, it may not be out of place, 

 during the hour before us, first, briefly to 

 inquire into the present state of evolution 

 and its usefulness to zoologists as a working 

 theory, and then to dwell more at length on 

 the subject of the effect of geological changes 

 on animal life. 



The two leading problems which confront 

 us as zoologists are: What is life ? and 

 How did living beings originate? We 

 must leave to coming centuries the so- 

 lution of the first question, if it can ever be 



*Address of the Vice-President before Section F. — 

 Zoology — of the American Association for the Ad- 

 vanement of Science, August 22, 1898. 



solved ; but we can, as regards the second, 

 congratulate ourselves that, thanks to 

 Lamarck, Darwin and others, in our day 

 and generation, a reasonable and generally 

 accepted solution has been reached. 



Time will not allow us to attempt to re- 

 view the discoveries and opinions which 

 have already been discussed by the founders 

 and leaders of the different schools of evo- 

 lutionary thought, and which have become 

 the common property of biologists, and are 

 rapidly permeating the woi'ld's literature. 



It may be observed at the outset that, if 

 there is any single feature which differen- 

 tiates the second from the first half of this 

 centurj', it is the general acceptance of the 

 truth of epigenetic evolution as opposed to 

 the preformation or incasement theory, 

 which lingered on and survived until a late 

 date in the first half of the present century.* 



*The theory of incasement [emiottment) , pro- 

 pounded by Swammerdam in 1733, was that the 

 form of the larva, pupa and imago of the insects 

 pre-existed in the egg, and even in the ovary, and 

 that the insects in these stages were distinct animals 

 contained one inside the other, like a nest of boxes, 

 or a series of envelopes one within the other ; or, in 

 his own words : "Animal in animali, seu papilio intra 

 erucam recondihis." Reaumur (1734) also believed 

 that the caterpillar contained the form of the chrys- 

 alis and butterfly, saying : ' ' Les parties des papillon 

 caehees sous le fourreau de chenille sont d'autant 

 plus faciles a trouver que la transformation est plus 

 proche. Elles y sont neanmoins de tout temps." 

 He also believed in the simultaneous existence of 

 two distinct beings in the insect. "II serait tres 

 curieux de connaitre toutes les communications in- 

 times qui sont entre la chenille et le papillon. '- * * 

 La chenille hache, broye, digere les aliments qu'elle 

 distribue au papillon ; comme les meres preparent 

 ceux qui sont portes aux foetus. Notre chenille en 

 uu mot est destinee a nourrir et a defendre le papillon 

 qu'elle renferme." (Tome i, 8'= Memoire, p. 363.) 



It was not until 1815 that Herold exploded this 

 error, though Kirby and Spence in 1828, in their In- 

 troduction to Entomology, combated Herold's views 

 and maintained that Swammerdam was right. As 

 late as 1834, a century after Swammerdam, Laoor- 

 daire, in his Introduction a I'Entoraologie, declared 

 that ' a caterpillar is not a simple animal, but com- 

 pound,' and he actually goes so far as to say that ' a 



