7-8 EX VIRIBUS VIVIMtrS.' 



food is abundant, for waters 'team with life' truly- 

 more than the atmosphere. Terrestrial animals, whilst 

 supporting themselves mostly on the ground, live in 

 the air, and in very few cases is their food to be 

 found abundantly in this medium, and accordingly 

 their expenditure in getting food is greater. Thus 

 among Vertebrata, the Whale is long-lived, the Cro- 

 codiles and Chelonians are long-lived, the Salaman- 

 droids and the Fish. It does not appear certain that 

 the Batrachia (Frogs and Toads) are shorter lived 

 than the Salamandroids ; their terrestrial habits in- 

 volve greater expenditure, but their very much higher 

 individuation may counterbalance this. Among In- 

 vertebrata, the Mollusca are long-lived ; the Pul- 

 monata less so than the branchiate Gasteropods. 

 Paludina and Lymnseus living in the same pond 

 differ thus in age,i whilst no land Mollusc is as 

 large (and therefore probably from what we have 

 seen as long-lived) as many hundreds of aquatic 

 (marine) species. 



The aquatic Arthropods (Crustacea), excluding the 

 minuter forms, are most broadly contrasted with the 

 terrestrial Insects, Myriapods, and Arachnids, in re- 

 spect of length of life, as we have before mentioned, 

 and set forth in the list. Descending lower, we find 

 no terrestrial groups to compare.^ 



' As far as the writer's observations go, Lymnseus lives four years, 

 and Paludina seven or eight. 



^ There is the terrestrial leech, and there are the terrestrial Planarise, 

 or ground Flukes, the longevity of which is not ascertained. 



