AN ESSAY ON LONGEVITY. 79 



Reptiles living in hot countries,, and feeding on 

 large masses of food at intervals, have . small ex- 

 penditure and live long. The higher Reptiles are the 

 most sluggish and inert of any animals in proportion 

 to their degree of development ; and hence, their 

 expenditure being small and their development high, 

 we should expect them to exhibit great longevity, 

 which they do. A very instructive contrast is af- 

 forded by Birds and Reptiles, which are so closely 

 allied in structure. The active, expending Birds are 

 short-lived as compared with such Reptiles as the 

 Tortoise and Crocodile. 



Echinoderms, being exceedingly sluggish, living 

 on the most easily obtainable food, in many cases, 

 viz. the organic matter diffused in sand, live longer 

 than would be expected from their comparatively 

 low place in the scale of life. Actinia, which is 

 also almost like a vegetal as to absence of personal 

 expenditure, as are other sedentary ccelenterates, 

 owes its great longevity to a relatively high evolu- 

 tion, in respect of integration. It buds never (or 

 rarely), and breeds sexually but little. 



The parasitic worms and Crustacea might be ex- 

 pected to have a great longevity from the total 

 absence of personal expenditure ; but here, as in 

 many plants, there is enormous generative expendi- 

 ture, which shortens life, the small percentage of 

 those born which ever get into the happy conditions 

 of a stomach or gill, being the reason for this great 



