ORGANIC STRUCTURE : MORPHOLOGICAL 29 



Concrete and brick — clayey and cementing substances resisting 



crushing stresses ; 

 Gold and platinum ornaments — partially because these metals 



do not tarnish ; 

 Spider silk — fine and strong protein filaments capable of making 



traps ; 

 Urea — a residue resulting from a metabolic tendency or a synthetic 



chemical substance. All such are obviously artifacts ; 

 and so on. 



//. ORGANIC STRUCTURE : MORPHOLOGICAL 



A very great number of organisms, collected at random, can 

 easily be arranged in categories, w^hich we may here call species 

 (but see Section 77). These categories are such that all the 

 organisms in any one of them resemble each other much more 

 closely than they resemble the organisms in any one of the other 

 categories. 



So that, given a great deal of experience, a systematist can 

 generally refer any organism, collected at random, to its natural 

 category. (That is, in respect of some large group of species 

 well-known to the systematist, for organic nature is so rich in 

 forms that it is not possible for anyone to acquire such an intimate 

 knowledge of all forms of life.) This recognition of the specific 

 position of any organism is based on inspection, simply, or assisted 

 by the microscope, or supplemented by dissection : chemical 

 structure, or morphology, is studied experimentally. 



Groups of categories, that is, genera, families, classes and 

 phyla of organisms, can be constructed (see Section 77). All 

 the species in any genus resemble each other more closely than 

 they resemble the species in any other genus. So also with the 

 genera that can be grouped into a family, the families that are 

 grouped into orders, and so on. 



The species (or some other more elementary category (see 

 Section 77^) is a natural category of organisms. Other and more 

 general categories are logical constructions. The individuals 

 grouped into a species are actually and always dissimilar, in detail, 

 to each other, but here we neglect this individual variability. 

 Because of individual variability, and of transformism, the number 

 of organic forms is indefinitely great. 



