EVOLUTION, CYTOLOGY AND MENDEL'S LA^VS. 223 



Organisms are not made up merely by the few characters enumerated 

 by the S3'stematist ; an infinite number of differing relations of parts 

 might be formulated. Evolutionary divergence is not confined to 

 external adult characters, but may appear in any structure, function 

 or instinct, and at any time in the life history. Species very different 

 as adults may have closely similar young, or larvae may be much more 

 diverse than the mature insects. Only the inadequacy of our notions 

 of the vital structure and activities has led us to expect that repro- 

 ductive cells will be found to contain special 'hereditary mechanisms' 

 for the predetermination of the characteristics of adults. The largest 

 and most complex individuals are still groups of cells, and no adequate 

 reason has been shown for believing that particular cells or links of 

 the organic sequence are more hereditary or more determinant than 

 the others. Characters are to be thought of as lines of biological 

 motion, not as structures or entities of reproductive cells. The pre- 

 determination of the infinity of structural and morphological char- 

 acters and positional relations of the millions of cells of the adult by 

 a working model resulting from the conjugation of sexual elements 

 may be dismissed as a crudely anthropomorphic notion of biological 

 processes, as unsupported by facts as it is illogical in conception. Cells 

 have their functions and organs, but evolution is not confined to these; 

 it is also a supercellular or organic process. Cytology is a very inter- 

 esting branch of descriptive biology, but it enjoys no special evolution- 

 ary facilities. 



Polycellular organisms grow by the division of cells; but instead 

 of proving that all cells divide in the same way cytologists have found 

 that the same result may be accomplished by a great variety of pro- 

 toplasmic organs and processes. Unicellular organisms are known to 

 be extremely diverse cytologically, and the cells of compound organ- 

 isms are, if possible, more so. We know also that the diversity of 

 organisms is not due so much to differences of the individual cells as 

 to differences of number and arrangement in the cell-colonies of which 

 they are constituted. 



Heredity is the unknown means by which successive generations of 

 organisms are able to construct themselves in similar, though not iden- 

 tical, forms ; it is, in short, an organic memory, and is responsible, not 

 alone for the repetition of the structural type, but also for vast num- 

 bers of involuntary functional coordinations and instinctive acts, 

 whether of unicellular or of compound organisms, or of whole colonies 

 of organisms. A colony of social termites is as truly an evolutionary 

 unit as a tree with its many branches, and the cooperative instincts 

 which pervade the individual insects are as truly a hereditary phe- 

 nomenon as the peculiar arrangement of branches which we term a 

 'character' of the tree. 



