INSECT EVOLUTION — CHETVERIKOV. 443 



gigantic forms as Maxtodonsawus, of which the skull alone was about 

 5 feet long. But with these gigantic forms the entire subclass of 

 Stegocephall dies out. 



The class of reptiles appears in the Permian period, and is here at 

 first represented by small primitive forms, which rarely exceed a half 

 meter in length {Palaeohatteria of Rynchocephalia, 50 cm. long; 

 Seymuria of Anomodontia, length of skull 10 cm.). Only in the 

 mesozoic, as the specialization of the first primitive characters de- 

 velops, do larger and larger and finally gigantic forms occur. 



Even in orders this relation may be followed out. Thus, in the 

 order Sauro pterygia the most primitive is the small Lariosaurus 

 (25-100 cm. long) and its highest specialization the order attained in 

 the huge Plesiosauri and Pliosauri, the skull of which is almost 1.3 m. 

 long. The order Dinosaurus, which always astounded human imagi- 

 nation by the abundance of gigantic, colossal, and most curious forms, 

 appears at first in the Triassic in the form of comparatively small and 

 primitive forms. Only later, in the upper Jurassic and in the chalk, 

 do the Dinosauri attain their greatest specialization and dimension 

 (Brontosaurus 17 m. long, upper Jura. ; Stegosaurus, 9 m. long, upper 

 Jura.; Iguanodon, almost 10 m. high, upper Jura, chalk; finally, 

 Triceratops, from the upper chalks with the largest skull that ever 

 existed on dry land, a length exceeding 2m.). But after that all of 

 these curious creatures rapidly die out. 



The mammalia also began their existence with insignificant sizes 

 (Amphilestes, Triconodon, and others), the length of which scarcely 

 exceeded that of a rat. But specialization proceeded gradually and 

 parallel with it also increase of size until there appeared such colossal 

 and in some respects highly specialized forms as Dinotherium, Masto- 

 don, mammoths, elephants, whales, etc. 



But enough of examples. It seems to me enough of these are 

 given to have the assertion I made above cease to appear as strange 

 as it might have seemed at first. The first impression, that the 

 evolution of the vertebrates proceeded from primitive large forms 

 to small ones, is false. On the contrary, we see the exact opposite: 

 Primitive forms are small and the massiveness of the animal body 

 grows only in course of evolution and specialization. If we should 

 now wish to answer the question made above — i. e., by what path did 

 the vertebrates travel toward self-preservation in the struggle for 

 existence ? — the answer will now be clear. It is the path of gradual 

 perfection, parallel with the accumulation of strength. This is the 

 path of open, direct force, but at the same time of honorable 

 struggle. The vertebrate faced danger; it did not run from it, 

 did not hide, and only developed its strength and power in the 

 process of perfection for the purpose of meeting the enemy. The 

 herbivor increased its body in order to place its mass in opposition to 



