THE ORGANISM AS A NATURAL THING ii 



a vast number of examples, and this number tends to become 

 indefinitely great without limit. 



There are very many categories of organisms and this number 

 tends (in the course of the evolutionary career) also to become 

 indefinitely great without limit. 



Although all organisms can be arranged in categories (such 

 as the species of the systematists) and although all the individuals 

 of a category can be recognized as belonging to that category, 

 yet all these individuals are, in some respects, different from each 

 other. 



it. Each kind of organism has an essential '' form.^^ This form 

 of body is characteristic and all the organisms contained in the 

 species exhibit it, and it is not exhibited by the organisms con- 

 tained in any other species. The form is so characteristic that 

 the species to which an individual belongs may be recognized 

 even when only a fragment of the body is seen. (These remarks 

 apply to species that we know very well. There is often difficulty 

 in recognizing the species of an organism, but this must be 

 regarded as due to our insufficient knowledge, or inexperience of 

 the species in question. The more intimately we know species 

 of animals the more characteristic do their forms appear to be.) 

 Hi. The ^^ form^^ of an organism is a career. That is, an 

 individual organism exhibits a passage from the embryonic phase, 

 through juvenescent and adult phases, towards senescence and 

 death. Its form is not the same in all these phases because it 

 undergoes a process of development from an original, initial and 

 undifferentiated phase in the ovum, or other beginning. Yet 

 the form, or structure, of the ovum, embryo, larva, young, mature 

 and senescent phases of the organism is always essential and 

 characteristic. It can be recognized as that of the species and 

 it may not be mistaken for any other species. 



iv. Organisms grow by selecting and reassembling the materials 

 of the medium in which they live. Crystals also grow by selecting 

 materials from the medium (or mother-liquor) in which they are 

 placed, but this is not the same kind of process as that of organic 

 growth. The materials, or molecules, which compose the sub- 

 stance of a crystal are chemically similar to those which exist in 

 the mother-liquor, whereas the materials of the body of an 

 organism are not the same as the materials in its medium. For 

 instance, the materials of the body of a green plant are water, 



