DEVELOPMENT HYPOTHESES. 203 



and then to maintain that the fish-embryo, for example, 

 acted upon by extremely favourable conditions, might be 

 developed beyond itself into a reptile, or the reptile into a 

 bird, is assuming a doctrine of which we have no proof, 

 and merely stating, in perverted terms, the grand physiolo- 

 gical fact of animal gradation and affinity. Besides, it is 

 an argument that cuts both ways. If an embryo, under 

 favourable conditions, can be developed beyond its own 

 parent species, it may also, under unfavourable conditions, 

 be retarded and thrown back into the grade that lies be- 

 neath it ; and as external conditions varied during the 

 geological epochs now genial and now obnoxious we 

 ought to have degradation as well as development. The 

 great gradational progress taught by geology being always 

 steadily from higher to higher, is. however, against this ; 

 and when a species or family is subjected to obnoxious 

 conditions, it invariably dwarfs and dies out in its ow T n 

 proper character a trilobite as a trilobite, an ammonite as 

 an ammonite, an ichthyosaur as an ichthyosaurus and never 

 under the guise of a lower order. All, too, that we know 

 of existing nature is against this doctrine of transmutation 

 species and genera remaining (under the restricted limits 

 of variation) as fixed and permanent now as they were 

 known to the Ninevites and Egyptians four thousand 

 years ago. 



It is argued, no doubt, that the transmutational advances 

 from species to species take place by slow and imperceptible 

 stages, which cumulatively become apparent only after the 

 lapse of ages. Admitting, however, this rate of progress, 

 there ought still to be transitional forms in various stages 

 of progress at every epoch forms w T hich we fail to perceive 

 in the living world, just as geology has failed to detect 

 them in that which has become extinct. Again, the modi- 

 fications for which the developist contends are those of a 



