Numher of Living Animals at two different periods. Ill 



conjecture that the law of increase indicated by the oak of 333 

 years in ny Tabic, is followed by this one, though evidently 

 older. If, therefore, we calculate the age of the oak in Well- 

 beck Lane, we see by the thickness of that of 333 years, that 

 it must have been about 1300 years old when Evelyn lived, and 

 more than 1400 in the year 1/75. 



5. Lastly, in cases where it is impossible to obtain a trans- 

 versal cut of an old tree, it may happen that we may have an 

 opportunity of making a lateral cut in the tree, in order to 

 ascertain how much it has increased in a given number of years, 

 and in this way find out the minimum of its mean increase. It 

 Avas by this process that Adauson discovered the age of the 

 Baobabs ; he saw the extent of the growth of these trees in 

 three centuries, and also knowing the growth of young trees, he 

 was enabled, by striking an average, to establish the general 

 law. The a^-e of the Taxodiuin of Chapultepec in Mexico 

 should be carefully investigated by this plan. 



By means of the five plans, either singly or connected, which 

 I have just pointed out, we may arrive at a knowledge of the 

 age of old exogenous trees in a manner sufficiently accurate for 

 the object of this inquiry. Let us now point out the trees to 

 which it is principally to be directed. The greatest longevity 

 in the vegetable kingdom oiisht to be found, 1st, In trees which, 

 by their hardness, incorruptibility, or size, should most power- 

 fully resist inclement seasons ; 2d, In countries which are not 

 exposed to ice, or to other causes which too frequently ter;d to 

 destroy large plants. 



A Table shoiolng the numher of known living Species of 

 Animals at two different 2'>eriods. 



Sperie% Vrinwn to Species l;Hown to 



Liiiiiffius ill 17/6. Naturalists in 1833* 



Mammalia 221 1,100 



Birds 904 6,500 



Amphibia 204 1,500 



Fishes 376 7,000 



MoIliiscJi 832 5,000? 



Aiinelicles ..^. 50 315 



(.'rustacea...c Ill 1,500 



Arachnida 97 3,000 



Insecta 2616 50,000 



Enthelmintha 15 1,500 



Radiaria 46 280 



Medusaria 11 208 



Polj'pi or Zoophyta .... 131 536 



Rotatoria 8 ». 119 



lufusotia S u.... 291 



