490 . METAMORPHOSIS OF ORGANISMS. 



being, depend on the particular physical conditions under which the 

 growth is taking place. The germ which is to produce a lichen obtains 

 from materials around it the substances it wants as best it may; but 

 the germ which is to end in the development of man is brought in suc- 

 cession under the influence of many distinct states. As a consequence 

 of this, it gives rise in succession to a series of animated forms, which, as- 

 suming by degrees a higher complexity, end at last in the perfect human 

 being. At one time it was believed that these metamorphoses, as they 

 are termed, are limited to insects and frogs : the insect, which at first 

 appears under the form of a caterpillar as it comes from the egg, and, 

 passing through the pupa state, at last takes its true position as a wing- 

 ed being ; the frog, which, appearing at first from the ovum as a true 

 fish, whose respiration is carried forward by gills, and whose life is lim- 

 ited to the water, at last assumes a new constitution and a new organi- 

 zation, breathes by lungs, and becomes an amphibious reptile. But it 

 is now known that these, so far from being exceptions, are only instances 

 of a general rule, which is, that all organized beings shall begin existence 

 at the bottom of the scale, and, taking on one type of life after another, in 

 more or less rapid succession, end, finally, in assuming a size and form 

 analogous to those of the parent which gave them birth. 



There is a general resemblance between the life of an individual and 

 the life of a species. Each has its time of birth, its time of maturity, 

 its time of decline ; each also has its embryonic states. The fossil forms 

 of the early geological ages are in many cases the embryos of existing 

 animals. Upon each all natural agents have exerted their effects, push- 

 ing forward or retarding development ; and this applies not only to an- 

 imals, but also to plants : it is in accordance with the principles we are 

 setting forth that over the whole domain of life natural forces exert 

 their sway. Change the conditions under which growth is taking place, 

 and you at once change resulting form and function. It is in this man- 

 ner that, on a small scale, the horticulturist works in furnishing us what 

 are called improved varieties of flowers and fruits. It is in this manner 

 that animals, known to have been indisputably of the same original kind, 

 assume such different forms and characters in various climates. It is 

 true, we can not expect in an abrupt mariner to bring about such strik- 

 ing modifications in a solitary individual, for the life of an individual is 

 readily destroyed, but not so the life of a race ; and Nature, carrying on 

 her operations in the slow lapse of centuries, and dealing with races 

 rather than individuals, forces them up to any point of development she 

 may desire, but still the impress of the laws under which they have been 

 brought to that condition is upon them, and each betrays, in the embry- 

 onic and foetal forms, a manifestation of the metamorphoses through 

 which his race has run. 



