380 



PRINCIPLES AND METHODS OF PALAEONTOLOGY. 



Bat it is obvious that if once the influence of hereditary transmission 

 in modifying the tendencies of the germ (and no one denies it) be ad- 

 mitted, it is very difficult to say where the modification of a given species 

 shall stop. 



Here, therefore, is the battle ground of those who admit and those 

 who deny the indefinite modifiability of species. On the one side are 

 adduced the two indubitable facts, firstly, that certain unquestionable 

 modifications of one and the same species, such as the dog, are, as 

 Cuvier says, more difterent than any wild species of the same natural 

 genus; secondly, that the admission of indefiaite modifiability reduces 

 tlie production of species to the ordinary course of nature, and accounts 

 equally well for all the phenomena with any other hypothesis. 



On the other side are the equally unquestionable truths that specific 

 characters are retained uiuler even extreme modifying influences with 

 great tenacity, and that artificially produced modiflcations tend, if left 

 to themselves, to return, more or less nearly, to their primitiv^e specific 

 character. It may be doubted, however, if these proi>ositions are really 

 inconsistent with the doctrine of indefinite modifiability. 



At present the evidence before the naturalist can hardly justify Jiim 

 in declaring his absolute adhesion to either view, but according as he 

 inclines one way or the other, so will it be probable that his views as to 

 the limits of species will vary. He who leans to the hypothesis of indefi- 

 nite modifiability will tend to neglect, and he who inclines to that of 

 the fixity of species will tend to exaggerate, minute ditterences. As the 

 case now stands, those who wish to adhere to the golden mean must put 

 their trust in common sense, a perception of the needs of science, and 

 that sort of tact which can lie gained only by incessant practical work- 

 ing at species.* 



4. So much for those laws of natural history which help us to under- 

 stand what the various forms of living beings are, and how they vary. 

 The next most important question is, do animals and plants, as they die, 

 perish and leave no trace behind, or what becomes of them? 



The answer to this question must be ditt'erent according to the par- 

 ticular kind of animal or plant to which reference is made. The fungus, 

 which springs up in a night, dies, decays, and is swept away as rapidly ; 

 and the soft marine jelly-fish or worm may leave no more permanent 

 traces of its existence. Carnivorous and herbivorous animals, again, 

 destroy and eflace all recognizable signs of the existence of multitudes 

 even of those living beings which are, physically and chemically, better 

 (pialitied to endure. Again, though it be a fact that the great majorit;\- 

 of both animals and plants are provided with parts sufficiently hard and 

 indestructible to resist the ordinary causes of decay for a very consider- 

 able time, nevertheless exposure to damp and change of temperature in 

 the case of the remains of land animals, and the incessant wear and tear 

 of watery action among aquatic creatures, would sooner or later destroy, 

 or so deface as to render unrecognizable, the trunks of the hardest 

 wooded trees and the most solid bones and shells ; and this would take 

 place in a space of time which, however long to us, is a very brief period, 

 geologically speaking, were it not for the very sim|)le but efficient 

 preservative agencies which are brought into play by the very same 

 causes. 



The hard parts of terrestrial animals and the remains of land plants 

 are, indeed, to a great extent destroyed by their exposure to the coudi- 



* It should be noted that these pa^es Avere written before the appearance of Mr. 

 Darwin's book on the " Origin of Species," a work which has efiected a revolution iu 

 biological speculation. 



