8 THE HOUSE. 



found in the earliest members of the group which 

 afterwards possess them as, for example, the antlers 

 of deer, the horns of oxen or the rhinoceros, the 

 humps of camels, etc. (2) The suppression of parts 

 commonly present as the upper front teeth of rumi- 

 nants, the tails of bears and guinea-pigs, the outer 

 toes of the horse's foot, the entire hind limbs of por- 

 poises, etc. (3) The modification of the form, size, 

 and relation of parts as the immense development 

 of the tusks in the walrus and male musk-deer, the 

 complicated foldings of the grinding teeth of ele- 

 phants, etc. 



In tracing out any series of gradual modifications 

 following each other in a regular chronological se- 

 quence, as we are sometimes fortunate enough to be 

 able to do,* we find that progress is usually from the 

 general to the special. It must not, however, be sup- 

 posed from this statement that all animals living 

 in ancient times were more generalized in character 

 than many now existing. On the contrary, many 

 of the extinct forms, even those of quite early 

 periods, were in some portion of their structure 

 very highly specialized. In fact, high specialization 

 almost invariably leads ultimately to extinction, be- 



* Many such instances are described in an interesting se- 

 ries of works, entitled Les Encliainements du Monde Animal 

 dans les Temps Geologiques, by Professor Albert Gaudry, 

 Paris, 1878-90. 



