488 EXTINCTION OF FORMS. 



examination of some of these Indians from the highest regions. In these 

 we have, as we expected, found the lungs of an extraordinary dimension, 

 which the external form of the chest clearly indicated. We remarked 

 that the cells were much larger and more in number than in those of the 

 luHgs we had dissected in France ; a condition very necessary to increase 

 the surface in contact with the ambient fluid. To conclude, we have 

 discovered, 1st. That the cells were more dilated ; 2d. That their dilata- 

 tion increases considerably the volume of the lungs ; 3d. That, conse- 

 quently, they must have to contain them a larger cavity; 4th. That, 

 therefore, the chest has a much larger capacity than in the normal state ; 

 5th. That this great development of the chest elongates the trunk beyond 

 its natural proportions, and places it almost out of harmony with the 

 length of the extremities, this remaining the same as if the chest had 

 preserved its natural dimensions." 



With respect to the doctrine of the influence of physical agents on or- 

 Ar umentfrom g aju>za tion generally, we admit without hesitation that the 

 the extinction extinction of forms has been accomplished through outward 

 causes, decline of heat, etc. These extinctions are intimate- 

 ly connected with the appearance of new organisms, and, indeed, are to 

 be regarded as being, with them, essential parts of a common plan. It 

 would not appear agreeable to the mode in which the scheme of Nature 

 is carried out to invoke one class of influences for the removal of the 

 vanishing forms, and a totally different one for the introduction of the 

 new-comers. There seems to be a better harmony in the supposition that 

 all these things are managed upon similar principles, and that, since it is 

 the failure of congenial conditions which closes the term of life of a race, it 

 was the suitability of those conditions, or their conspiring together, which 

 gave it origin. 



The influence of decline of temperature appears when we examine par- 

 influence of ticular individuals or particular species either of plants or of 

 decline of tem- animals. Thus the Virginia cherry attains the height of 100 

 feet in the Southern States, and is dwarfed to a shrub of not 

 more than five feet at the great Slave Lake ; the nasturtium, which is a 

 woody shrub in warm climates, becomes a succulent annual in cold. Or, 

 if we examine some special tribe of life, as Milne Edwards has done in 

 the case of crustaceans, the higher the temperature, the greater the lia- 

 bility to variations of species, the more numerous also the differences of 

 form, and the attainment of a greater individual size. That these varia- 

 tions are the actual consequences of the physical conditions, and not 

 merely collateral results, is shown by supplying the condition that is 

 wanting. We can imitate the natural result, in an artificial way, in hot- 

 houses ; the plants of the warmest climate may be grown, and the effects 

 of summer imitated at any season of the year. What better proof could 



