AND PHYSIOLOGY OF THE BRITISH ASSOCIATION. 70 1 



existing animals are descended have in most instances perished ; 

 and although there is no reason why they should not have been 

 preserved in a fossil state, yet, owing to the imperfection of the 

 geological record, palaeontology is not so often of service as 

 might have been hoped. 



While, for the reasons just stated, it is not generally possible 

 to prove by direct observation that existing forms in their em- 

 bryonic state repeat the characters of their ancestors, there is 

 another method by which the truth of this proposition can be 

 approximately verified. 



A comparison of recent and fossil forms shews that there 

 are actually living at the present day representatives of a con- 

 siderable proportion of the groups which have in previous times 

 existed on the globe, and there are therefore forms allied to the 

 ancestors of those living at the present day, though not actually 

 the same species. If therefore it can be shewn that the em- 

 bryos of existing forms pass through stages in which they have 

 the characters of more primitive groups, a sufficient proof of our 

 proposition will have been given. 



That such is often the case is a well-known fact, and was 

 even known before the publication of Darwin's works. Von 

 Baer, the greatest embryologist of the century, who died 

 at an advanced age but a few years ago, discussed the pro- 

 position at considerable length in a work published between the 

 years 1830 and 1840. He came to the conclusion that the 

 embryos of higher forms never actually resemble lower forms, 

 but only the embryos of lower forms ; and he further main- 

 tained that such resemblances did not hold at all, or only to a 

 very small extent, beyond the limits of the larger groups. Thus 

 he believed that, though the embryos of Vertebrates might 

 agree amongst themselves, there was no resemblance between 

 them and the embryos of any invertebrate group. We now 

 know that these limitations of Von Baer do not hold good, but 

 it is to be remembered that the meaning now attached by em- 

 bryologists to such resemblances was quite unknown to him. 



These preliminary remarks will, I trust, be sufficient to de- 

 monstrate how completely modern embryological reasoning is 

 dependent on the two laws of inheritance and variation, which 

 constitute the keystones of the Darwinian theory. 



