PICTET*S PALJEONTOLOGY. 55 



physiologists are aware, that if two species are not very closely 

 allied, they will not breed together at all ; and that even if the spe- 

 cies are very near, but not identical, they produce hybrids which are 

 incapable of continuing their race and becoming the progenitors of 

 a modified form or new species. Every aberration from the type in 

 the way of crossing species is thus instantly stopped. 



" True it is, indeed, that the changes and varieties introduced in 

 domesticated species have been brought forward as an argument 

 against this conclusion ; but although such changes unquestionably 

 take place in horses, oxen, sheep, pigs and goats, and yet more re- 

 markably perhaps in dogs, where the form of the cranium becomes 

 modified, yet these very facts appear to me to furnish a conclusion 

 totally different from that which it has been attempted to draw. The 

 individuals the most widely removed from the primitive type never 

 present any real difference of form in the important organs. The 

 skeleton always exhibits invariable characters, as well with regard 

 to the number of the bones and their apophyses as to their relations 

 with one another, while the organs of nutrition, the nervous system, 

 and in short every distinctive peculiarity of organization is submitted 

 to the same law. The only marked difference exists either in the 

 absolute dimensions, a point known to be very variable, or in exter- 

 nal peculiarities yet more fugitive ; and with the exception of these 

 modifications in the form of the cranium, which we may easily sup- 

 pose to be connected with differences of instinct and to be the di- 

 rect result of education, it cannot be said that any one of the do- 

 mestic animals in its most extreme varieties loses the character of 

 the species. If therefore we find that the most energetic among 

 external agent?, — modifications of climate, of habit, of instinct and 

 of food, — have only been able during the lapse of ages to produce 

 some trifling change, which has not altered the type of the species, 

 are we not, from this examination of the domestic animals, justified 

 in believing the permanence of species rather than their transmu- 

 tation ? 



"And this view is the more probable, since the differences between 

 one fauna and another are very considerable ; and we have not to 

 treat of trifling modifications of a type, but rather of complete trans- 

 itions, often into very remote forms. Some naturalists indeed have 

 not shrunk from such consequences, and have asserted that the 

 reptiles of the secondary period owe their parentage to the palaeo- 

 zoic fishes, and were themselves the progenitors of the tertiary 

 mammals. Where is the physiologist who will admit such conclu- 

 sions ? and yet quite as much must be granted if it is attempted to 

 deduce all the geological faunas from an original one by the simple 

 transformation of species, and by means of a i)assage from one to 

 another, without the direct intervention of a creative power acting 

 at the commencement of each epoch. 



"And if for the production of such results it is assumed, contrary 

 to what we have supposed, that there have been great alterations of 

 temperature, and changes in the constitution of the atnios{)here, or 

 that nature in her early youth was more vigorous, the laws of physi- 



