AN ESSA V ON LONGEVITY. 75 



longer lived, for though in most cases possessing large 

 genital organs, they do not deposit their ova or sperm 

 so early or so rapidly as the Insects. The Vertebrata 

 are by no means prolific (except fish), and at the 

 same time are longer-lived than Invertebrata. 



Fish are long-lived, in spite of considerable gene- 

 rative expenditure,^ the explanation lying in the 

 diminished personal expenditure involved in their 

 aquatic life. This, too, affects greatly the case of 

 Annelids just quoted. Amongst Birds it is easy to 

 point out that smaller broods go with a greater lon- 

 gevity : thus the Eagle has but one or two eggs, the 

 common Owl four or five ; Finches two broods of five 

 in a season, and the Wrens and Tits eight to fifteen ; 

 and these, as appears from our list above, stand in the 

 same order as to longevity. It is very difficult indeed 

 to find particular cases in which the direct action of 

 generative expenditure on longevity is apparent, for it 

 affects other quantities before longevity, or its action 

 is counteracted by fluctuations in these quantities, as, 



' The bulk of the ova and sperm in fish is not so large as the number 

 of the ova lead one to think ; and moreover, as a rule, they give no 

 parental attention, which is a most important item of generative ex- 

 penditure. In those fishes which do, e. g. Pipe-fish, Hippocampus, and 

 Arius of the Amazons, the bulk and number of the ova is immensely 

 reduced. 



This item of parental attention is what in the case of man and other 

 animals tends much to balance the male and female generative expendi- 

 ture, for the male feeds both mother and young for a considerable time 

 by his exertion ; hence the female's expenditure of substance is in some 

 degree balanced. 



