OTHER THEORIES OF SPECIES-FORMING. 217 



(chemical units), units of a third order (physiological units) corn- 

 Spencer's posed of groups of molecules. These units are very 

 theory. small but very complex, and are the smallest masses in 

 which living substance can occur. Most of the micromeric theories, 

 which come after Spencer's, adopt this conception of a life-unit, very 

 small, but composed of an aggregate of molecules, and therefore 

 very complex. To his physiological units Spencer attributed a 

 polarity, wholly analogous with that possessed by the molecules 

 of crystalline substances. It is owing to this delicate, precise 

 polarity, varying of course with the varying molecular consti- 

 tution of the units, that they possess the capacity of actively 

 arranging themselves in the varied groupings normal to the parts 

 of the organisms. "Thus the resemblance is perfect between the 

 chemical polarity which causes crystallisation and that of the 

 physiological units which produces the form of organisms. In one 

 case the chemical molecules group themselves in a manner to form 

 an aggregate of definite but simple form, cubical, prismatic, 

 rhomboidal, with their parts arranged en tremies, aiguilles, croix 

 de Saint Andre, boulcs epincuscs, etc. In the other the units group 

 themselves in a body of a form less rigorously defined but which 

 may be very complicated: such as a plant or an animal." (Delage.) 



Of the theories in which the living units are assumed to be of 

 different kinds, and endowed with different functions, some assume 

 the units to be not directly representative of different cells or parts 

 of the body, while others assume this truly representative condition. 

 Of the first sort are a number of theories like those of Berthold. 

 Geddes, and others, in which the units are taken to be actual 

 chemical molecules, endowed with activity through special physico- 

 chemical properties or through purely chemical ones, \vhile still 

 others keep to the more usual type of a unit of a higher order 

 than a molecule, in which case also this unit is looked on as spe- 

 cially active because of particular electrical (Fol) or chemical 

 (Altmann and Maggi) or vital (Wiesner) endowment. But all of 

 these theories are much like each other and are much like Spencer's 

 theory in regard at least to the assumed units. Different, how- 

 ever, is the type of theory which introduces the assumption that 

 the fundamental life-units are directly representative of either 

 the specific cells, parts, or elementary characteristics of the organ- 

 ism. This is the kind of unit especially favoured by the men 

 who had, in their formation of a theory, a special eye to the 

 problem of heredity. How is the single germ-cell to be the bearer 

 of the "heredity" of the organism from which it comes? what 

 more simple to assume than that this cell shall be composed of 

 minute particles gathered from all the cells or groups of similar 



