ANNOTATIONS AND ADDITIONS. 303 



ment, and the whole vital process ; to all this must be further added 

 hygrometric influences and those of atmospheric electricity. 



My investigations respecting the numerical laws of the distribu- 

 tion of forms may possibly be applied at some future day with 

 advantage to the different classes of Rotiferse in the animal creation. 

 The rich collections at the Museum d'Histoire Naturelle in the 

 Jardin des Plantes at Paris, already contained, in 1820 (according 

 to approximate estimations), above 56,000 phsenogamous and crypto- 

 gamous plants in herbariums, 44,000 insects (a number doubtless 

 too small, though given me by Latreille), 2500 species of fish, 700 

 reptiles, 4000 birds, and 500 mammalia. Europe has about 80 

 species of indigenous mammalia, 400 birds, and 30 reptiles. In the 

 Northern temperate zone, therefore, the species of birds are five times 

 more numerous than those of mammalia, as there are in Europe five 

 times as many Compositaa as there are Amentaceee and Coniferse, 

 and five times as many Leguminosse as there are Orchideae and Eu- 

 phorbiacse. In the southern hemisphere, the ratio of mammalia is in 

 tolerably striking agreement, being as 1 to 4.3. Birds, and still 

 more reptiles, increase in the number of species, in approaching the 

 torrid zone, more than the mammalia. Cuvier's researches might 

 lead us to believe that the proportion was different in the earlier 

 state of things, and that many more mammalia had perished by re- 

 volutions of Nature than birds. Latreille has shown what groups 

 of insects increase towards the Pole, and what towards the Equator. 

 Illiger has given the countries of 3800 species of birds according to 

 the quarters of the globe : it would have been much more instruc- 

 tive if the same thing had been done according to zones. We should 

 find little difficulty in comprehending how, on a given space of the 

 earth's surface, the individuals of a class of plants or animals limit 

 each other's numbers/or how, after long-continued contest and many 

 fluctuations caused by the requirements of nourishment and mode 

 of life, a state of equilibrium should be at last established; but the 

 causes which have limited not the number of individuals of a form, 

 but the forms themselves, in a particular space, and founded their 

 typical diversity, are placed beneath the impenetrable veil which still 

 conceals from our eyes all that relates to the manner of the first 

 creation and commencement of organic beings. 



