16 HYATT ON THE TERTIARY SPECIES 



physical causes represented by that term acted upon the organization of the animals 

 unfavorably, occasioned a weak pathological condition leading to deterioration in size, 

 and to the production of senile-like characteristics and deformities, and the final but 

 gradual extinction of the different sub-species. In other publications I have used the 

 term geratology, and shall employ that same term here to indicate such correspondences ' 

 and such phenomena. 



Having met the question of the general retrogtession in size and form, by the 

 hypothesis of an unfavorable environment, the question naturally arises, how shall we 

 account for the progression of the progressive series ? How then could this environment 

 act upon such closely allied shells, in such an opposite way as to cause the decease of some 

 races and be entirely healthy for others ? 



We habitually refer such questions among animals, and in man, to the innate strength 

 or phability of the constitution of the race or the individual, and account for the survival, 

 growth, and development of races and individuals by this reference to their supposed 

 ability either to resist change in their surroundings, or to become modified in accordance 

 therewith. 



This principle is one of the best established results of paleontological research. It is 

 founded primarily upon the perpetual dying out of races in geological times, simultaneously 

 with the close of formations and the incoming of closely-allied, but modified forms in 

 later formations. It is sustained by the existence of persistent types which resisted change 

 to such a degree, that they are but slightly modified through long periods of geological 

 time, although passing through revolutions in the environment which destroyed the larger 

 proportion of their allied forms. It is sustained by the advent and comparatively short life 

 of those forms, which suffer greater modifications in each successive formation. Among 

 living animals it is a matter of daily experience to find some races incapable of 

 enduring variations in the surroundings, to which others readily accommodate themselves, 

 and even thrive under. Precisely the same environment, therefore, may produce 

 results diametrically opposed to each other, even upon different individuals of the same 

 species or closely allied forms, provided there is anything in the constitution either 

 directly acquired or inherited, which enables the organization of one to resist or fit itself 

 to conditions which the other cannot healthfully endure. It being therefore a matter of 

 fitness or unfitness of the organization, a question of inherited or acquired power and 

 capacity, which we can refer to the constitution of individuals, species, or races, we must 

 now inquire, whether there are any signs of greater strength to encounter, or ability to 

 accommodate themselves to change manifested in progressive series. The facts already 

 stated show this. The individual shells are larger, steadily increase in size in the suc- 

 cessive species of . each series, and show distortion only in isolated individuals as the 

 results of disease, or only in the very advanced age of others equally exceptional. This 

 latter fact is very curious, and would be puzzling if I had not already been familiar with the 

 extraordinary fact, that many animals have no old age ; e. g., Amoeba, most of the Insecta, 

 and probably most of the Crustacea. Old age, in fact, being the result of an exhausted 

 or outgrown organization, it can onlj^ take place in animals which have complicated 

 organs, and which also live so long, or use them so actively that they become worn out 

 by perpetual effort to sustain the waste occasioned by their surroundings. The absence 



