94 'DETERMINANTS' VERSUS 



complexity of function, and in proportion as distinct functions are 

 performed by special parts of the organism, so are the several 

 parts more and more bound together into one organic whole. 



This difference is well seen between plants and highly-organised 

 animals. The plant, it is true, develops seeds and pollen in special 

 parts or organs ; but just as the plant, taken as a whole, is to a 

 great extent a repetition of similar parts whose organisation is by 

 no means so complex, so do these separate parts, when severed 

 from the parent organism, retain that generative power which 

 enables them, under suitable conditions, to grow into plants of a 

 similar kind. But in animals even comparatively low in the scale 

 of complexity all this is changed. They are not mere repetitions 

 of similar parts — each having a potential individuality of its own : 

 they are rather aggregations of different parts bound together and 

 constituting one organic whole by means of vascular and nervous 

 systems which serve as bonds of unity. The higher the grade of 

 development of the organism — the more its tissues have become 

 differentiated — the less are they severally endowed with a repro- 

 ductive power, even of a partial kind. In such organisms, we find 

 that each part has a distinct function to perform, and therefore the 

 reproductive function is restricted to the elements produced in 

 definite organs. Although restricted in their place of origin, how- 

 ever, there is reason to believe that sperm-cells and germ-cells are 

 comparatively unspecialised products. After a careful summary of ■ 

 what is known on the subject, H. Spencer says : — " The assumption 

 to which we seem driven by the ensemble of the evidence is, that 

 sperm-cells and germ-cells are essentially nothing more than 

 vehicles in which are contained small groups of the physiological 

 units in a fit state for obeying their proclivity towards the structural 

 arrangement of the species they belong to. . . . Thus, the pheno- 

 mena of Heredity are seen to assimilate with other phenomena ; 

 and the assumption which these phenomena thrust on us appears 

 to be equally thrust on us by the phenomena of Heredity. We 

 must conclude that the likeness of any organism to either parent is 

 conveyed by the special tendencies of the physiological units 

 derived from that parent. In the fertilised germ we have two 

 groups of physiological units, slightly different in their structures. 

 These slightly different units severally multiply at the expense of 

 the nutriment supplied to the unfolding germ, each kind moulding 

 the nutriment into its own type. Throughout the process of 

 evolution the two kinds of units mainly agreeing in their polarities 



