386 MR.W.H. FLOWER ON THE SKELETONS OF WHALES [Noy. 8, 
the adult (e. g. Bulenoptera rostrata, Mus. Roy. Coll. Surg., 17! 
long; Physalus antiquorum, The Hague, 40' long; Megaptera lon- 
gimana, Leyden, 283! long; ditto, Louvain, 33! long). This stage 
of growth may be designated as “young”; towards its close the 
majority of the bones lose the spongy character of the ‘‘ very young” 
animal, and acquire the firm structure characteristic of succeeding 
ages.—II. In the next stage, both epiphyses of the humerus, those 
of the upper end of the radius and ulna, and those of the bodies of 
the anterior cervical and the posterior caudal vertebree are united, 
while those of the greater part of the column are still free. The 
ossification of the transverse processes of the cervical vertebrze, 
although often still incomplete at the ends, has gone on so far as to 
give them in great measure the characteristic form seen in the adult. 
This is a condition in which skeletons are frequently seen in museums. 
The animal while in this stage, which may be called “ adolescent,” 
has attained nearly its full size (Balenoptera rostrata, Mus. Roy. 
Coll. Surg., 25’ long; Balena mysticetus, ibid., 47'; ditto, Brussels, 
50'; Megaptera longimana, ibid., 46'); the reproductive functions 
have also come into action (Balena mysticetus, 2, Mus. Roy. Coll. 
Surg., pregnant).—III. The last stage, or the perfectly “adult,” 
in which all the vertebral epiphyses are ankylosed, I have met with 
among the Baleenoidea only in the large Fin-Whales of the common 
species mentioned before. Adult Hyperoodons and other Delphi- 
noids are not uncommon in collections. 
It is possible that variations may occur in different species or dif- 
ferent individuals in the order of completion of the several parts of 
the skeleton. The foregoing observations are founded upon a careful 
examination of upwards of twenty skeletons of Whalebone Whales 
of different species. If not complete, they at least indicate a line of 
inquiry important to the exhaustive study of the anatomy and zoology 
of the Cetacea. 
The next point to which I would draw attention is the amount of 
variation found among different individuals of the same species—a 
point which will assist greatly in determinmg what differences in 
similar specimens may be considered as specific; and yet it is one 
which cannot absolutely be settled until the limits of the species 
themselves are definitely fixed. Some years ago, when many species 
which we now know to be very different were thrown together into 
one, the individuals of a supposed species were found to vary ex- 
tremely among themselves. It is possible that the same error may 
be made at present, and species still confounded which more critical 
examination will show to be distinct. We must feel our way cau- 
tiously, and I shall therefore under this heading only take for illus- 
tration some of the best-known and most generally accepted species, 
and see what can be derived from an examination of some of their 
best-marked characteristics. 
First, as to variations in size. It will help much in determining 
specific identity of new or little-known species, if we can show, among 
those that are well known, what is the usual amount, and what the 
limit, of variation in this direction ; for we may assume that it is at 
