REPORT OF AMERICAN COMMISSIONERS. 347 



anniliilated ; and if more than a certain numbe]' Birth-rate aud 



death-rate. 



of deaths occur at that early period, the destruc- 

 tion of the species is only a question of time. 

 Given, therefore, a species comprising a certain 

 number of individuals, that number will tend 

 upward or downward or will remain constant, 

 according to the relation of births to deaths. In 

 nature, where the conditions for a certain species 

 are favorable, the usual course is that the num- 

 bers increase until by the increase of tlieir nat- 

 ural enemies, or the less favorable character of 

 the conditions (usually less favorable by reason 

 of insufficient food supply resulting from increase 

 in numbers), the birthrate and deathrate become 

 equal, after which the number will remain con- 

 stant until some new influence makes its appear- 

 ance to afi*ect them favorably or unfavorably. 

 This is the condition which the seals would 

 unquestionably reach in time, if not interfered 

 with by man, and which, undoubtedly, they 

 have reached at various times in their history. 

 Under this condition certain numbers of seals are 

 born every year and the same number die every 

 year, the total number alive at any one time 

 depending on the distribution of the deaths 

 among seals of various ages. 



