16 The Problems 



a germ-cell, the hope of seeing pollen grains differentiated 

 according to the characters they bear is probably remote. 

 Better hopes may perhaps be entertained in regard to 

 spermatozoa, or possibly female cells.] 



As an objection to the deduction of purity of germ-cells, 

 however, it is to be noted that though true intermediates 

 did not generally occur, yet the intensity in which the 

 characters appeared did vary in degree, and it is not easy 

 to see how the hypothesis of perfect purity in the repro- 

 ductive cells can be supported in such cases. Be this, 

 however, as it may, there is no doubt we are beginning to 

 get new lights of a most valuable kind on the nature of 

 heredity and the laws which it obeys. It is to be hoped 

 that these indications will be at once followed up by 

 independent workers. Enough has been said to show how 

 necessary it is that the subjects of experiment should be 

 chosen in such a way as to bring the laws of heredity to a 

 real test. For this purpose the first essential is that the 

 differentiating characters should be few, and that all avoid- 

 able complications should be got rid of. Each experiment 

 should be reduced to its simplest possible limits. The 

 results obtained by Galton, and also the new ones especially 

 described in this paper, have each been reached by restricting 

 the range of observation to one character or group of char- 

 acters, and it is certain that by similar treatment our 

 knowledge of heredity may be rapidly extended. 



To the above popular presentation of the essential facts, 

 made for an audience not strictly scientific, some addition, 

 however brief, is called for. First, in regard to the law of 

 Ancestry, spoken of on p. 5. Those who are acquainted with 

 Pearson's Grammar of Science, 2nd ed. published early in 



