428 THE GERM-PLASM 



determinants than those of the original feather were exposed to 

 selection. It was stated above that fluctuations in the structure 

 of the determinants, caused by inequalities of nutrition, may 

 also be produced in consequence of their more rapid growth and 

 earlier division. If, then, certain determinants for the feather 

 of the original form underwent division at an early stage in 

 individual males, so that their number became doubled, a 

 lengthening of the feather must have resulted as soon as the 

 doubling occurred in the majority of the ids. The majority 

 need not have appeared in one individual from the first, but, 

 like every other simple variation of a determinant, it may have 

 originated sporadically, in separate ids of different individuals, 

 and have become increased by the repetition of the process 

 of amphimixis in every generation. The modification would 

 become apparent and the processes of selection could take place, 

 as soon as these ids had attained a majority in any individual. 



2. Pathological Variation 



The above theoretical explanation of the 'increase' of a 

 character possesses the important advantage of accounting for 

 the sudden appearance of .more extensive variations. If more 

 abundant nourishment can cause the doubling of a determinant 

 in the germ-plasm, it is possible, and even probable, that many 

 or all the contiguous determinants for the same feather will 

 become doubled. The feather must consequently at once in- 

 crease to twice the size. Doubts have often been justly raised 

 as to whether the process of sexual selection at first produces 

 very slight variations, which would scarcely be noticed and 

 preferred by the selecting sex. We learn from the doctrine of 

 determijiants that it is unnecessary to take such minute varia- 

 tions into account, and that more extensive ones may suddenly 

 arise directly from the germ-plasm. 



The doubling by division, not only of biophors and deter- 

 minants, ids and idants, but even of individual groups of 

 congncent determinants^ such as must be contained in the 

 germ-plasm in the form of primary constituents of any organ — 

 e.g., a feather — is theoretically possible. But this is one of the 

 more special questions, the details of which may be reserved 

 for subsequent investigations. I think it is highly probable 

 that many congenital deforfnities, such as the occasional 

 doubling of the tarsus in the hind-limbs of beetles and other 



