62 ORGANIC EVOLUTION — THE FACTORS 



mediate units, which we may term ^physiological. 

 There seems no alternative but to suppose that the 

 chemical units combine into units immensely more 

 complex than themselves, complex as they are;' and 

 that in each organism, the physiological units produced 

 by this further compounding of highly compound 

 atoms, have a more or less distinctive character. We 

 must conclude that in each case, some slight difference 

 of composition in these units, leading to some slight 

 difference in the mutual play of forces, produces a 

 difference in the form which the aggregate of them 

 assumes." — Principles of Biology, vol. i. pp. 182-3. 



" . . the assumption to which we seera driven by 

 the ensenible 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."— 76id pp. 254-5. 



" If the assumption of a special arrangement of parts 

 by an organism is due to the proclivity of its 

 physiological units towards that arrangement, then 

 the assumption of an arrangement of parts slightly 

 different from that of the species, implies physiological 

 units slightly unlike those of the species, and these 

 slightly -unlike physiological units, communicated 

 through the medium of sperm cell or gerjn cell, will 

 tend, in the offspring, to build themselves into a 

 structure similarly diverging from the average of the 

 species." — Jbid. p. 245. 



" The repair of a wasted tissue may therefore be 

 considered as due to forces analogous to those by which 

 a crystal reproduces its lost apex, when placed in a 

 solution like that from which it was formed. In either 

 case, a mass of units of a given kind shows a power of 

 integrating with itself diffused units of the same kind ; 

 the only difference being that the organic mass of units 

 arranges the different units into special compound 

 forms, before integrating them with itself. .... 



