VON BAER AND RISE OF EMBRYOLOGY. 



12 1 



the ' Comparative Embryology ' he went to Switzerland for recupera- 

 tion, and met his death, with that of his guide, by slipping from an 

 Alpine height into a chasm. His death occurred in July, 1882. His 

 portrait is shown in Fig. 11. 



The memorial edition of his works fills four quarto volumes, but 

 the ' Comparative Embryology ' is Bal- 

 four's monument, and will give him en- 

 during fame. It is not only a digest of 

 the work of others, but contains, also, 

 general considerations of a far-seeing- 

 quality. He saw developmental proc- 

 esses in the light of the hypothesis of 

 organic evolution. His speculations 

 were sufficiently reserved and nearly 

 always luminous. It is significant of 

 the character of this work to say that the 

 speculations contained in the papers of 

 the rank and file of embryological work- 

 ers, for more than two decades, and often 

 fondly believed to be novel, were for the 

 most part anticipated by Balfour, and 

 also better expressed, with better qualifi- 

 cations. 



The reading of ancestral history in the stages of development is 

 such a characteristic feature of the embryological work of Balfour's 

 period that some observations concerning it will now be in place. 



Interpretation of the Emory ological Record. — Perhaps the most 

 impressive feature of animal development is the series of similar 

 changes through which all pass in the embryo. The higher animals, 

 especially, exhibit all stages of organization from the unicellular 

 fertilized ovum to the fully formed animal so far removed from it. 

 The intermediate changes constitute a long record, the possibility of 

 interpreting which has been a stimulus to its careful examination. 



Meckel, in 1821, and later Von Baer, indicated the close similarity 

 between embryonic stages of widely different animals; Yon Baer, 

 indeed, confessed that he was unable to distinguish positively between 

 a reptile, bird and mammalian embryo in certain early stages of 

 growth. In addition to this similarity — which is a constant feature 

 of the embryological record — there is another one that may be equally 

 significant, viz., in the course of embryonic history, sets of rudimentary 

 organs arise and disappear. Rudimentary teeth make their appear- 

 ance in the embryo of the whalebone whale, but they are transitory and 

 soon disappear without having been of service to the animal. In the 

 embryos of all higher vertebrates, as is well known, gill-clefts and gill- 

 arches, with an ajmropriate circulation, make their appearance, but 



Fig. 11. Francis M. Bai.four 

 (1851-1882). 



