( cxvii ) 



destruction that the organic world as we see it is maintained. 

 Production of new beings is, of course, the necessary material 

 for destruction to work on, but it need not here detain us 

 long. Only let me offer the practical remark that the life 

 history of a species cannot be considered complete unless it 

 records such an important factor as the limits of the number 

 of young that proceed from a single female parent, a number 

 among some Lepidoptera far surpassing a thousand, among 

 others much less than a hundred. Moreover, as effective 

 production requires that there shovild be surrounding condi- 

 tions which afford opportunities for the previous union of the 

 parents, and admit of the disposition to use those opportuni- 

 ties, such as appropriate temperature and the right degree of 

 light or obscurity, particulars of these conditions should be 

 recorded.* 



Destructive forces. 



The forces of destruction will occupy us much longer. 

 Individuals are always being produced in abundance, their 

 numbers being kept down by wholesale slaughter, a term in 

 which I include starvation by the consumption of their food. 

 Fully 99 per cent, of the offspring of an ordinarily prolific 

 year-lived species are annually slain before their lives have 

 become sufliciently complete to leave posterity, so that an 

 investigation into the reason why their numbers persist 

 involves an inquiry into the fatalities which they suffer, and it 

 is to these fatalities consequently that it is of cardinal import- 

 ance that attention should be directed. To complete their 

 life history there must thus be added a detailed death history. 



Want of food. 

 The first of the causes of fatality that will be noticed is 



* A few famous words, used iu a very different sense, happen so 

 concisely to sum up these requirements that I venture to re-quote them 

 from a little paper published more than forty years since, humbly pray- 

 ing the forgiveness of all Dante scholars : 



"lor parenti 



. . il luogo, il tempo e il seme 

 Di lor semeuza e di lor nascimenti." 



