220 NATURAL SCIENCE. April, 



inquiries should be conducted without hypotheses as to the function of 

 the organs involved. But when a result like the present result has been 

 obtained, it seems to us that the inquiry has only been begun ; that 

 Professor Weldon's method concerns itself merely with the fact that 

 in certain cases there is a relation between selective destruction and 

 certain specified dimensions. The question as to whether such small 

 dimensions have, or do not have, a selection-value for the animal 

 remains to be answered. Having got so far, it remains for the 

 statistical method to investigate all the correlations that exist between 

 variations of frontal breadth and variations of other organs and parts. 

 When the correlations are known, then it will be the part of another 

 method, an experimental method dealing with function, to determine 

 upon which, if upon any, of the correlated variations selection acts. 

 The minute deviations of frontal breadth may be associated with 

 functional differences of a much larger order, as the minute move- 

 ments of the index of a pressure-gauge are associated with enormous 

 and potent changes of pressure. Professor Agassiz suggested that 

 deviations in the adult might only be the record of selective destruc- 

 tion operating upon earlier larval stages. In this case there seems 

 little probability of such a view being applicable, for the destructive 

 selection did not set in until late in life, and only after an increase in 

 deviations had been recorded. But, to our mind, nothing is more 

 certain than that the corollary of Professor Weldon's method is a 

 detailed study of the correlations that exist between this deviation 

 that he has shown to have a relation to the death-rate, and an experi- 

 mental investigation into each associated change, until there has 

 been found the functional variation upon which the selective destruc- 

 tion actually operates. Pending such inquiry, Professor Weldon 

 may be taken to have shown that there is a relation between selec- 

 tion and minute variations, not that selection operates upon minute 

 variations. 



Variations and Mutations. 



In a valuable paper, contributed to the American Journal of Science 

 for November, 1894, W. B. Scott discusses the question of variation. 

 Like many others, he considers that Mr. Bateson's book on variation 

 would have been much more useful, and its suggestion very different, 

 had Mr. Bateson made use of the facts accumulated by palaeonto- 

 logists. The great point made by Professor Scott is the clear distinc- 

 tion between individual and phylogenetic variation. " Remembering 

 that the significant fact in the history of a group is not so much the 

 character of its variations at any one stage, as the gradually shifting 

 positions successively occupied by the normal or centre of stability, 

 we find that any mammalian series at all complete, such as that of 

 the horses, is remarkably continuous, and that the progress of 

 discovery is steadily filling up what few gaps remain. So closely do 



