GENERAL CONSIDERATIONS. 983 



ura? selection, whereby those animals that are the strongest and best adapted 

 for the special conditions of life present at any time, supplant, and ulti- 

 mately exterminate the less perfectly constituted, has at length culminated 

 in a creature that even now, howsoever noble in reason and infinite in facul- 

 ties, yet presents a transitory condition only to some more exalted phase of 

 existence. The facts on which this opinion rests are of various character and 

 weight, and a few only of the more important can here be alluded to. We 

 have seen that in the earliest stages of the development of the embryo of the 

 Human subject, which in this respect presents a character common to all 

 animals, a single cell is alone discoverable ; this receiving an accession of 

 energy from the sperm-cell, and being placed under favorable conditions 

 for the acquisition of the materials requisite for growth, soon undergoes 

 subdivision ; and in the cellular mass thus formed a differentatiou of parts 

 takes place, by which the various organs and tissues of the body are succes- 

 sively evolved. In the higher forms of the animal creation we have further 

 seen, that at certain transitory stages of development a close analogy exists 

 with the permanent conditions of creatures occupying a lower position in 

 the scale; and that, whilst throughout the whole a wonderful unity in the 

 process is clearly discernible, each species presents certain characteristic 

 features which are peculiar to itself. This, it is supposed, may have occur- 

 red in the history of the world. A few great types may have been originally 

 formed, which, in the lapse of ages, owing to the action of external agents, 

 as light, heat, and food, and to the perpetuation of accidental varieties 

 especially adapted to these external conditions, have gradually resulted in 

 the infinitely varied species that now surround us. 1 With this extraordinary 

 similarity in the process of development throughout the whole animal king- 

 dom, which seems very difficult to account for upon the theory of a separate 

 creation for each species, it cannot be a matter of surprise that close bonds 

 of alliance should be found in the adult period of life even amongst the 

 most dissimilar creatures. The Birds, for instance, appear to be a sin- 

 gularly well-defined and separate group ; yet the researches of Mr. Parker 2 

 have shown that in their osseous system they possess affinities with every 

 other class of the Vertebrata; so that, whilst presenting the closest analogies 

 to Reptiles, and especially to the Lacertilian group, they anticipate, on the 

 one hand, various Mammalian characters, and on the other recede, as it 

 were, below Reptiles, retaining different Ichthyic points of structure, which 

 are not, as a rule, found in that class. And thus it has ever been found, that 

 the more closely the structure of even the most aberrant forms of animal 

 life has been investigated, the wider have been the affinities discovered, often 

 explaining what was previously obscure in the structure of others, whilst at 

 the same time the more complete has been the proof that no real isolation 

 of a species, much less of a genus or family, exists. It is indeed probable 

 and this is a point on which Mr. Darwin lays great stress that were it pos- 

 sible to reproduce the entire series of forms now become extinct, a regular 

 gradation would be presented from the lowest to the highest ; and hence that, 

 as Dr. Hooker has maintained, 3 we are indebted for our means of resolving 

 plants into limitable genera and orders simply to the extinction of the forms 

 by which they were originally connected. The reason that the intermediate 

 links have not been discovered, is owing essentially to the imperfection of 

 the geological record. Of that great book, comparatively few leaves have 



1 For a full exposition of this theory, see Darwin, On the Origin of Species by 

 Moans of Natural Selection, etc., 1859. 



2 See his paper on the Osteology of the Gallinaceous Birds and Tinnamous, in the 

 Trans, of the Zoological Society for Nov. 25th, 1862. 



3 Introduction to the Flora of New Zealand, 1853. 



