288 STUDIES IN THE EVOLUTION OF ANIMALS 



One cannot look at the drawings of fishes, even of a restricted 

 region, such as that of India, by Francis Day, without feeling that 

 monstrous forms must have been generated among fishes in plenty. 

 Agassiz, in the account of his Joiirney in Brazil, gives us a 

 striking tale of the innuinerable species of fishes he and his 

 assistants discovered in the Amazon and its tributaries. 



If experiments in teratogeny be worth anything, they will 

 certainly modify our notions of the origin of species, solely by slow 

 accumulation of some minute variation. Just think of it ; the 

 ovum segments into two and then into four cells, and so on. If 

 any injury should occur to any one of these cells, from whatever 

 cause, the result may be a monstrosity. The wonder is that we 

 are not all monsters ! We say heredity keeps us straight ; we 

 might also say it keeps us crooked, to allow for variations ; but 

 when these statements are translated into common language they 

 seem to spell — ' we know nothing about them ' ! 



A little more atomic disturbance here, a little less there, during 

 the embryonic stage, may produce a new compound, which then 

 may be called a species, a genus, or even an order, as the case may 

 be. Naturalists may think they have discovered all the species in 

 a district, but new ones may be naturally manufactured now and 

 then, just as the chemist produces new compounds by manipulating 

 and acting upon old ones. 



There cannot be much doubt that the action of the nerve-centre, 

 in co-operation with the vaso-motor nerves which affect the 

 nourishment of parts, may cause the degeneration, atrophy, and 

 eventual suppression of an organ. 



Let us suppose, for instance, a Dinosaur of the ordinary kind, 

 with fore-legs sufficiently large to enable it to move on all-fours, 

 say, like a Kangaroo. Let us suppose again that by a sudden 

 monstrosity the fore-limbs were dwarfed to the size of those oi Cerato- 



