518 
THE GEOLOGIST. 
According to these views, eTery vertebrate skeleton is divided into 
a number of transverse segments, perpendicular to the general direction 
of the vertebral column or back-bone, each segment of the neck, the 
back, and the tail, comprising a single vertebra, and each segment of 
the head comprising a bone analagous to a vertebra. Immediately- 
above the central bone of each vertebra (the spinal column being sup- 
posed horizontal) is the sjnnal canal, axtending from the head to the 
tail, and containing the spinal-chord, which is a continuation of 
the mass, constituting the brain, the cavity of the skull being re- 
garded as no expansion of the spinal canal; and so with the limbs, and 
throughout the entire organized frame, each segment of the body, 
however modified, being ragardad as the homological equivalent of each 
and every of the others. 
The opposition of the early transcendentalists to the doctrine of 
final causes — as the argument of Cuvier, of the adaptation of the organs 
to the fulfilment of pre-ordained and special purposes is called — has con- 
tributed to create a suspicion in the minds of many persons that all 
such generalizations of the phenomena of organic life were inimical to 
the latter doctrine, and tend to the notion that the adaptions and har- 
monies of the adajytive modifications are in subservience to the general 
laws. This mode of expression ought rather to be inverted, and it should 
be asserted that these laws were impressed upon matter in subservience 
to the ends to be obtained. Mr. Hopkins hence goes on to specula- 
tions on the future conditions of our planets. " The character of a 
geologist," he says, " is essentially that of a historian ; but it is im- 
possible for him, at times, not to assume something also of a prophetic 
character, and endeavour to stretch his mental gaze into the far future, 
as he habitually directs it to the remote periods of the past. In ven- 
turing such speculations in regard to the future of our globe, even those 
extended chronological conceptions of time, which the contemplation of 
geological phenomena has given, must be enlarged, and we must look 
forward to times indefinitely more distant than those to which we may 
have hitherto looked in our most remote anticipations of the future." 
As in the past history of the earth we have seen the important in- 
fluence of heat, so, in turning to the future of our planet, we are led 
first to inquire what may hereafter be expected to result from that uni- 
versal agent in physical change ? and on this topic Mr. Hopkins con- 
cludes " that the terrestrial heat is probably at presont, or must be 
hereafter, reduced so as no longer to be of sufficient intensity to produce 
a recurrence of those stupendous upheavals and dislocations which 
have taken place in past times. 
The principal argument against the notion of any diminution of 
intensity in the causes of such movements is based on the fact that some 
of the existing mountains — the Alps, for example — do not date from an 
earlier period than the early Tertiaries. 
The next consideration is the future change of climatal conditions. 
The mean annual temperature of the earth's surface depends on solar 
and other external influences, the temperature of the surrounding pla- 
netary space, and the constitution of the earth's atmosphere. 
It must, also, manifestly depend in part on the central heat, assuming 
such to exist. The mathematical solution of the problem tells us that 
