THE ORIGIN OF SPECIES 147 



of their skins, or bones, or other lifeless exuvia ; that we 

 are acquainted with none, or next to none, of their physio- 

 logical peculiarities, beyond those which can be deduced 

 from their structure, or are open to cursory observation ; 

 and that we cannot hope to learn more of any of those 

 extinct forms of life which now constitute no inconsiderable 

 proportion of the known Flora and Fauna of the world : 

 it is obvious that the definitions of these species can be only 

 of a purely structural or morphological character. It is 

 probable that naturalists would have avoided much con- 

 fusion of ideas if they had more frequently borne the 

 necessary limitations of our knowledge in mind. But 

 while it may safely be admitted that we are acquainted 

 with only the morphological characters of the vast majority 

 of species the functional, or physiological, peculiarities of 

 a few have been carefully investigated, and the result of 

 that study forms a large and most interesting portion of 

 the physiology of reproduction. 



The student of Nature wonders the more and is astonished 

 the less, the more conversant he becomes with her opera- 

 tions ; but of all the perennial miracles she offers to his 

 inspection, perhaps the most worthy of admiration is the 

 development of a plant or of an animal from its embryo. 

 Examine the recently laid egg of some common animal, 

 such as a salamander or a newt. It is a minute spheroid 

 in which the best microscope will reveal nothing but a 

 structureless sac, enclosing a glairy fluid, holding granules 

 in suspension. But strange possibilities lie dormant in 

 that semi-fluid globule. Let a moderate supply of warmth 

 reach its watery cradle, and the plastic matter undergoes 

 changes so rapid and yet so steady and purposelike in* 

 their succession, that one can only compare them to those 

 operated by a skilled modeller upon a formless lump of 

 clay. As with an invisible trowel, the mass is divided and 

 subdivided into smaller and smaller portions, until it is 

 reduced to an aggregation of granules not too large to 

 build withal the finest fabrics of the nascent organism. 

 And, then, it is as if a delicate finger traced out the line to 

 be occupied by the spinal column, and moulded the contour 

 of the body ; pinching up the head at one end, the tail at 

 the other, and fashioning flank and limb into due sala- 

 mandrine proportions, in so artistic a way, that, after 

 watching the process hour by hour, one is almost involun- 

 tarily possessed by the notion, that some more subtle aid 



