THE VEGETABLE AND ANIMAL KINGDOMS. 113 



^ithin-door life for several generations they assimilate 

 to the whites amongst whom they live. On the other 

 hand, there are authentic instances of a people originally 

 well-formed and good-looking, being brought, by imper- 

 *sct diet and a variety of physical hardships, to a mean- 

 er form. It is remarkable, that prominence of the jaws, 

 a recession and diminution of the cranium, and an elong- 

 ation and atenuation of the limbs, are peculiarities always 

 produced by these miserable conditions for they indicate 

 an unequivocal retrogression towards the type of the 

 lower animals. Thus we see nature alike willing to 

 go back and to go forward. Both effects are simply the 

 result of the operation of the law of development in the 

 generative system. Give good conditions, it advances ; 

 bad ones, it recedes. Now, perhaps, it is only because 

 there is no longer a possibility, in the higher types of 

 being, of giving sufficiently favorable conditions to carry 

 on species to species, that we see the operation of the law 

 so far limited. 



Let us trace this law also in the production of certain 

 classes of monstrosities. A human foetus is often left with 

 one of the most important parts of its frame imperfectly 

 developed : the heart, for instance, goes no farther than 

 the three-chambered form, so that it is the heart of a rep- 

 tile. There are even instances of this organ being left in 

 the two-chambered or fish-form. Such defects are the re- 

 sult of nothing more than a failure of the power of deve- 

 lopment in the system of the mother, occasioned by weak 

 health or misery. Here we have apparently a realization 

 of the converse of those conditions which carry on spe- 

 cies to species, so far, at least, as one organ is concerned 

 Seeing a complete specific retrogression in this one point, 

 how easy it is to imagine an access of favorable conditions 

 sufficient to reverse the phenomenon, and make a fish 

 mother develop a reptile heart, or a reptile mother de- 

 velop a mammal one. It is no great boldness to surmise 

 that a super-adequacy in the measure of this under-ade- 

 quacy, (and the one thing seems as natural an occurrence 

 as the other) would suffice in a goose to give its progeny 

 the body of a rat, and produce the ornithorynchus, or 

 might give the progeny of an ornithorynchus the mouth 

 and feet of a true rodent, and thus complete at two stages 

 the passage from the aves to the mammalia. 



Perhaps even the transition from species to species does 



