ILLUSTRATIONS OF DEVELOPMENT. 509 



tially tentative, it gives us very base notions of the manner Base nature of 

 in which natural operations are conducted, since we can not ^ew oniw or- 

 divest ourselves of the idea that such a passage from imper- ganic world. 

 fection to perfection implies trial, verification, and improvement : a pro- 

 cess which, though it is suited to the limited knowledge of man, is not 

 in accordance with the precision, perfection, and energy of Nature, and is 

 to "be rejected the moment we consider that we deal with the acts of 

 Omniscience and Omnipotence. Moreover, that erroneous view leads to 

 fallacious estimates, both in the animal series and in the individual, of 

 the character of transitory forms, conferring on them too much inde- 

 pendence, and therefore too much dignity; for the transitory forms of 

 embryonic life and the forms of animal species are the equivalents of 

 each other. 



Every living being, therefore, springs from a germ, which will develop 

 itself into the likeness of its parent, provided it is submit- career and stop- 

 ted to the same conditions through which, its parent pass- P a s e of a devel - 

 ed ; but if the conditions be changed, it will either take pen ds on exter- 

 on a new aspect, or if they have become incompatible, it nal condltlons - 

 will cease to exist. Similarity of development depends on similarity of 

 condition, as is abundantly proved by such instances as the almost per- 

 fect resemblance of the two sides of the body, which, in reality, may be 

 regarded as distinct individual forms. To the proof thus derived from 

 bilateral symmetiy as occurring in man might be added such suggestions 

 as arise from the well-known resemblance of twins ; and as identity of 

 condition will thus give origin to analogy of development, so we may 

 fairly infer that difference of condition, no matter in what respect the dif- 

 ference may be, will give rise to difference of structure ; thus experienced 

 gardeners have shown that the sex of flowers is, to a very great extent, 

 determined by the brilliancy of the light in which they grow. Differ- 

 ence in the supply of nutritive material removes the spines from one 

 plant, or doubles the flowers of another, by changing its stamens . into 

 petals, or alters the cycle of career, and makes annuals into biennials. 

 As illustrations of the complete changes of form during development, 

 241. the three following cases may be 



presented : in Fig. 241 are shown 

 the ova of the frog, which are trans- 

 parent spherical bodies, containing 

 a dark globule. From this, by de- 

 velopment, the tadpole, which is a 

 true fish, breathing by gills, arises. 



Development of the frog. The figures represent a side and 



upper view. After growth has taken place to a certain degree, a change 

 of structure becomes apparent, limbs gradually emerging, and the ani- 



