178 
POPULAK SCIENCE BEVIEW. 
pigeons, Mr. Darwin urges the extreme probability that all the domestic 
breeds of rabbits have been derived from one ancestor. He then shows 
what cautious observation is exercised to determine the minute variations 
and the necessity for careful pairing in order to avoid reversion. On all 
these particulars his remarks are of the highest interest. But in regard to 
the alterations in the skeleton, we think the domestic rabbits afford conclusive 
testimony. The changes in the bones of these animals are of the gi’avest 
character. The bones of the limbs have increased in weight in proportion 
to the weight of the body. With the increased size of the body the third 
cervical vertebra has assumed characters proper to the fourth cervical and 
the eighth and ninth dorsal vertebras have similarly assumed characters 
proper to the tenth and posterior vertebrae. The skull in the larger breeds 
has increased in length. The brain appears to have decreased in size. The 
supra-orbital processes of the frontal bones and the free end of the malar 
bones have increased in breadth, and in certain breeds the occipital foramen 
differs from that of the wild rabbit. In like manner, the scapulae, the bones 
of the ear, palate, and jaw, have, by processes of correlation, become highly 
variable and modified. The facts which w'e have quoted upon the history 
of two races will be found multiplied in Mr. Darwun’s book for every do- 
mestic family of animals and plants j and this part of the subject occupies 
the greater part of the first volume. 
The next points to be inquired into are those of variation, its laws and 
causes, and inheritance. These are discussed in the author’s second volume ; 
and their examination leads him to the remarkable hypothesis — Pangenesis, 
to which we have already referred. Starting with the proposition that 
the progeny of all animals displays variation — a proposition which it seems 
to us impossible to gainsay — the author proceeds to indicate the laws 
under which this tendency is governed. He thus formulates the following 
rules with respect to inheritance: — first, a tendency in every character, 
new and old, to be transmitted by seminal and bud generation, though often 
counteracted by various known or unknown causes; secondly, reversion 
or atavism, which depends on transmission and development being distinct 
powers ; it acts in various degrees and manners through both seminal 
and bud generation ; thirdly, prepotency of transmission, which may be 
confined to one sex or be common to both sexes of the prepotent form ; 
fourthly, transmission limited by sex generally to the same sex in which 
the inherited character first appeared ; fifthly, inheritance at correspond- 
ing periods of life, with some tending to the earlier development of the. 
inherited character. 
It is rather difficult to determine satisfactorily the opinion of the author 
on the question of the influences which determine variation in animals, as to 
whether, for instance, they are the result of what the older metaphysicians 
would style a natural tendency,” or are the consequence of the influence 
of external conditions. In one portion of his book he so distinctly opposes 
the theory of the operation of externals, that we are led to think he is 
of the metaphysical school. But then, further on, he so fully admits the 
effects of use and disuse in affecting the inheritance of certain qualities, 
and he so fairly acknowledges the inheritance of certain mutilations, such as 
those inflicted on rabbits by Dr. Brown- Sequard, that we are convinced 
