the Genera Tursiops, Orca, and Lagenorhynclius. 181 



and, in consequence, that in young individuals tliej must 

 present themselves in an abbreviated and comparatively un- 

 developed form ; and there are many other variations whicli 

 may be explained in an analogous manner. But the difficulty 

 commences when an aged individual behaves in one or more 

 particulars as if it was younger ; in other words, when one of 

 the features of organization which ordinarily accompany a 

 certain age or a certain size is deficient, or at any rate is in a 

 backward state — which of the two we do not at all know. Such 

 experiences are very valuable, not only to explain an isolated 

 case, but in general for the appreciation of the osteological 

 differences that we observe between individual and individual, 

 or between species and species ; and they are only arrived at 

 when we have sufficiently numerous materials to work upon. 

 Hence the necessityof not giving to Natural-History collections 

 too limited an extent, and the duty of seeking, by comparisons 

 judiciously made, to obtain general results which may be made 

 use of in analogous cases upon which the insufficiency of the 

 materials does not enable us to judge directly. I will cite a 

 few examples. The second of the first two cervical vertebrge, 

 which are soldered together in these animals, always presents 

 on each side a comparatively strong process or a transverse 

 ajiophysis, which, when completely developed, is pierced by a 

 large aperture ; in the young animal it is short and imper- 

 forate, the portion which surrounds the aperture being still 

 cartilaginous and no longer remaining in the skeleton when 

 this is macerated. But what are we to think when we find 

 that this part is nevertheless deficient in a skeleton which, by 

 its size and other peculiarities, shows that it is older than 

 another which possesses it ; or, what comes to the same 

 thing, that this formation appears in its full develbpment in a 

 skeleton which, in other respects, appears to be younger than 

 another which does not possess it ? The first piece of the 

 sternum, the manubrium sterni^ in the young T. tursio. as in 

 many other Dolphins, is furnished with an apophysis on each 

 side ; in old individuals this apophysis is soldered below to 

 the body of the manubrium by the ossification of a carti- 

 laginous or tendinous ligament, which then appears to be 

 perforated on each side by a round aperture. But how 

 surprised one is at finding in still older individuals this hole 

 opened out and converted into a notch, and the apophysis 

 free, although we might have expected to find the contrary 

 the case. 



In the young T. tursio the first five ribs are the only ones 

 w liicli have a double articulation with the thoracic vertebra}, 

 namely, by a tubercle with the transverse apophysis, and by 



