318 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



animals are in many cases very conspicuous and intelligible. 

 Thus, for instance, it is perfectly evident, and has long been 

 acknowledged, that by it a certain standard is fixed for the bulk 

 of the animal's body which cannot be exceeded without en 

 dangering the life of the individual. If, for instance, we grant 

 that the structure and specific gravity of any animal are factors 

 bearing a relation to each other that does not allow of any con- 

 siderable variation, and also admit the possibility of its growing 

 beyond the normal standard of size, the animal would finally 

 be so large that it could not move its own weight, since its 

 gravity must increase in geometrical progression. Of course the 

 maximum of height or length attainable by particular animals 

 varies with their organisation, and hence must differ in different 

 groups of animals. Birds are the most remarkable in this par- 

 ticular; in them the standard of bulk generally attainable 

 would be remarkably small with a specific gravity the same 

 as that of mammals, and their life in the air. But there 

 are in their organisation certain adaptations which make the 

 maximum bulk they actually attain tolerably high ; these are 

 the pneumatic bones and the air-cavities between the muscles 

 and in the body, which are sometimes extensively developed, 

 particularly in the strongest flyers, as for instance the Albatross. 

 By these the bird is enabled to attain a volume of which the 

 weight could not long be carried by the most powerful flyer if it 

 corresponded to that which any quadruped of the same size 

 would have to move. A very interesting illustration of this 

 peculiarity is afforded by one of Professor Marsh's latest dis- 

 coveries in America. The wonderfully rich deposits of fossil 

 remains in the Rocky Mountains have yielded to his search 

 a Reptile which, according to careful estimates, from a restora- 

 tion of its hind limbs, must have attained a height of at least 

 eighty feet. 



According to the calculation made by a mathematician a 

 friend of Professor Marsh's this creature would in that case 

 actually have exceeded the maximum size it could have con- 

 trolled, under the supposition that in general organisation, and 

 therefore in the specific gravity of its body and bones, it 

 exhibited no deviation from that of the largest reptiles now 



