128 
ANIMAL PEDIGREES. 
June, 1891. 
The palaeontological series thus agrees with the develop¬ 
mental series of stages through which the antlers of a stag 
pass at the present day before attaining their full dimensions. 
There is another point of view from which fossils acquire 
special interest in connection with the Recapitulation Theory. 
If the theory is correct, it must apply not merely to the 
animals now living on the earth, but to all animals that ever 
have lived; and it becomes a matter of considerable interest 
to enquire whether we have any evidence whereby we can 
test this point, and determine whether or not the fossil 
animals in their own individual development repeated the 
characters of their ancestors. 
At first sight the enquiry does not seem a promising one, 
for it may well be asked what possibility there is of deter¬ 
mining the embryology or mode of development of animals 
which are only known to us through the chance preservation 
of their bones or shells as fossils. 
In most cases, it is true that such determination is im¬ 
possible, but in some groups as, for example, the Trilobites, 
great numbers of well preserved specimens have been 
obtained, not merely of adults, but of young forms in various 
stages of growth ; and the study of these young forms has 
already yielded results of considerable interest. According 
to Barrande, to whom our knowledge of these early stages is 
mainly due, four chief types of development may be recog¬ 
nised, differing from one another much as existing Crusta¬ 
ceans do, in the relative size and perfection of the three 
regions, head, thorax, and tail, into which the body is divided. 
Evidence of a verv different kind, and often of far 
greater value, is afforded by the study of shells, whether of 
Mollusca or of Foraminifera. Such shells, like those of 
Orbitolites already noticed, have no power of interstitial 
growth, and increase in size can only be effected by the addi¬ 
tion of new shelly matter to the part already in existence. 
In most instances these additions take place in such manner 
that the older parts of the shell are retained unaltered in the 
adult; and examination of the adult or fully formed shell 
will then reveal the several stages through which the shell 
passed in its development. 
In such a shell, for instance, as Nautilus or Ammonites, 
the central chamber is the oldest or first formed one, to which 
the remaining chambers are added in succession. If, there¬ 
fore, the development of the shell is a repetition of ancestral 
history, the central chamber should represent the palieonto- 
logically oldest form, and the remaining chambers, in succes¬ 
sion, forms of more and more recent origin. 
Ammonite shells present, more especially in their sutures, 
and in the markings and sculpturing of their surface, charac¬ 
ters that are easily recognised. Upwards of four thousand 
