X^: BIOLOGICAL THEORIES. 579 



cycles. Only one generation in each cycle consists of males and 

 females. 



5. Hybrids frequently, though not always, exhibit the characters 

 of both parental types blended together. Not infrequently they bear 

 a closer resemblance to a more remote ancestor than to their 

 immediate ancestors (atavism). 



6. Though some cells divide, like Amoeba, into two like halves, 

 cell-division not infrequently results in the production of cells which 

 are unlike each other, e.g., Vorticella, segmenting ovum (after the first 

 two or three divisions). 



With reference to Variation, it must be borne in mind that — - 



1. Slight variation is almost universal. 



2. Conspicuous variation, though less widespread, is very 

 marked in certain species and under certain conditions. 



3. Conspicuous variation is in some cases more noticeable in the 

 larva than in the adult. This is especially true of some caterpillars. 



4. An individual which differs conspicuously from all its near 

 relatives, not infrequently bears a closer resemblance to remote 

 ancestors (atavism). 



5. Variation is often very great under domestication and under 

 the influence of a changed environment. 



* * * ^c 'Jfi 



The schools of Pangenesis and of Continuity alike regard 

 heredity as the original and normal course of events, and variation 

 as a secondary and abnormal occurrence brought about by the for- 

 tuitous interference of some extraneous influence. Even modern 

 text-books speak of " heredity " and " variability " as if they were con- 

 crete entities capable of producing effects. One would laugh at the 

 philosopher who sought to explain the turning of a weather-cock to 

 the south-east on a particular occasion by referring it to the bursting 

 into activity of a long-latent tendency to turn to the south-east. The 

 *' tendency to vary " and the " phylogenetic force " of some writers, 

 the "force of heredity" and "force of variability" of others, are 

 equally absurd. T. J. Parker says' ^^ Heredity ... is modified by 

 Variability,'" and earlier writers are not less slip-shod in their 

 treatment of these and allied subjects. 



It is, however, not so much this blundering between the abstract 

 and the concrete that I wish to emphasise, as the unanimity with 

 which heredity has been regarded as the primitive, and variation as 

 the modified phenomenon. This aspect of current views may be 

 illustrated by comparing heredity to the regular movement of a planet 

 in its orbit, and variation to a deviation of that planet from its orbit 

 through the attraction of some larger body or bodies passing near it. 



I propose to turn all this upside down, and looking upon varia- 

 tion as a phenomenon of greater antiquity than heredity, to consider 



1 " Elementary Biology," iSgi.p. 145. 



2P 2 



