400 THE ZOOLOGIST. 



from this arrangement, which morphologically is undoubtedly inferior 

 to the unpaired, azygous, &c, modifications. The fact that newts 

 exist is proof that they are efficient in their way. Such orthogenetic 

 changes are as predictable in their results as the river which tends 

 to shorten its course to the direct line from its head waters to the 

 sea. That is the rivers Entelechy and no more due to purpose or 

 design than is the series of improvements from the many gill-bearing 

 partitions of a shark to the fewer, and more highly finished comb- 

 shaped gills of a Teleostean fish. 



The success of adaptation, as measured by the morphological 

 grade of perfection reached by an organ, seems to depend upon the 

 phyletic age of the animal when it was first subjected to these 

 •' temptations." The younger the group, the higher is likely to be 

 the perfection of an organic system, organ, or detail. This is not a 

 platitude. The perfection attained does not depend merely upon the 

 length of time available for the evolution of an organ. A recent 

 Teleostean has had an infinitely longer time as a fish than a reptile, 

 and this had a longer time than a mammal, and yet the same problem 

 is solved in a neater, we might say in a more scientifically correct, 

 way by a mammal than by a reptile, and the reptile in turn shows 

 an advance in every detail in comparison with an amphibian, and so 

 forth. 



A few examples will suffice : — 



The claws of reptiles and those of mammals ; there are none in 

 the amphibians, although some seem to want them badly, like the 

 African frog Gampsosteonyx, but its cat-like claws, instead of being 

 horny sheaths, are made out of the sharpened phalangeal bones which 

 perforate the skin. 



The simple contrivance of the rhinocerotic horn, introduced in 

 Oligocene times, compared with the antlers of Miocene Cervicomia 

 and these with the response made by the latest of Euminants, the 

 hollow-horned antelopes and cattle. The heel-joint ; unless still 

 generalised, it tends to become intertarsal (attempted in some 

 Lizards, pronounced in some Dinosaurs and in the Birds) by fusion 

 of the bones of the tarsus with those above and below, so that the 

 tarsals act like epiphysial pads. Only in mammals epiphyses are 

 universal. Tibia and fibula having their own, the pronounced joint 

 is cruro-tarsal and all the tarsals could be used for a very compact, 

 yet non-rigid arrangement. The advantage of a cap, not merely the 

 introduction of a separate pad, is well recognized in engineering. 



Why is it that mammalian material can produce what is denied 

 to the lower classes ? In other words, why are there still lower and 

 middle classes ? Why have the}' not all by this time reached the 

 same grade of perfection ? Why not indeed, unless because every 

 new group is less hampered by tradition, much of which must be 

 discarded with the new departure ; and some of its energy is set free 

 to follow up this new course, straight, with ever growing results, until 

 in its turn this becomes an old rut out of which a new jolt leads once 

 more into fresh fields. 



