TRANSACTIONS OF SECTION D. 831 
Of cases where a single specimen has sufficed to prove the paleontological 
significance of a developmental character, Archeeopteryx affords a typical example. 
In recent birds the metacarpals are firmly fused with one another and with the 
distal series of carpals; but in development the metacarpals are at first, and 
for some time, distinct. In Archzeopteryx this distinctness is retained in the 
adult, showing that what is now an embryonic character in recent birds, was 
formerly an adult one. 
Other examples might easily be quoted, but these will suffice to show that the 
relation between Paleontology and Embryology, first enunciated by Agassiz, and 
required by the Recapitulation Theory, does in reality exist. There is much yet 
to be done in this direction. A commencement, a most promising commence- 
ment, has been made, but as yet only a few groups have been seriously studied 
from this standpoint. 
It is a great misfortune that paleontology is not more generally and more 
seriously studied. by men versed in embryology, and that those who have so greatly 
advanced our knowledge of the early development of animals should so seldom 
have tested their conclusions as to the affinities of the groups they are concerned 
with by direct reference to the ancestors themselves, as known to us through their 
fossil remains. 
I cannot but feel that, for instance, the determination of the affinities of fossil 
Mammalia, of which such an extraordinary number and variety of forms are now 
known to us, would be greatly facilitated by a thorough and exact knowledge of the 
development, and especially the later development, of the skeleton in their existing 
descendants, and I regard it as a reproach that such exact descriptions of the later 
stages of development should not exist even in the case of our commonest domestic 
animals. 
The pedigree of the horse has attracted great attention, and has been worked 
at most assiduously, and we are now, largely owing to the labours of American 
palzontologists, able to refer to a series of fossil forms commencing in the lowest 
Eocene beds, and extending upwards to the most recent deposits, which show a 
complete gradation from a more generalised mammalian type to the highly 
specialised condition characteristic of the horse and its allies, and which may 
reasonably be regarded as indicating the actual line of descent of the horse. In 
this particular case, more frequently cited than any other, the evidence is entirely 
paleontological. The actual development of the horse has yet tobe studied, and 
it is greatly to be desired that it should be undertaken speedily. Klever’s? recent 
work on the development of the teeth in the horse may be referred to as showing 
that important and unexpected evidence is to be obtained in this way. 
A brilliant exception to the statement just made as to the want of exact know- 
ledge of the later development of the more highly organised animals is afforded 
by the splendid labours of Professor Kitchen Parker, whose recent death has 
deprived zoology of one of her most earnest and single-minded students, and 
zoologists, young and old alike, of a true and sincere friend. Professor Parker's 
extraordinarily minute and painstaking investigations into the development of the 
vertebrate skull rank among the most remarkable of zootomical achievements, and 
afford a rich miue of carefully recorded facts, the full value and bearing of which 
we are hardly yet able to appreciate. 
If further evidence as to the value and importance of the Recapitulation 
Theory were needed, it would suffice to refer to the influence which it has had 
on the classification of the animal kingdom, Ascidians and Cirripedes may be 
quoted as important groups, the true affinities of which were first revealed by 
embryology ; and in the case of parasitic animals the structural modifications of the 
adult are often so great that but for the evidence yielded by development. their 
zoological position could not be determined. It is now indeed generally recog- 
nised that in doubtful cases embryology affords the safest of all clues, and that the 
zoological position of such forms can hardly be regarded as definitely established 
unless their development, as well as their adult anatomy, is ascertained. 
1 Klever, ‘Zur Kenntniss der Morphogenese des Equidengebisses,’ Momphologisches 
Vahrhuch xv. 1889, p. 308. 
