238 NATUEAL HISXOKY" SOCIETY OF DUBLIN. 



flew into it, and others dashed themselves against the rocks on which 

 the fire was lighted, although these birds were rarely seen in the day- 

 time. This shows that these birds are nocturnal in their habits when 

 near land : at sea, however, they are much more common in the day-time 

 than at night, and 1 have never heard of one of them, or any other Petrel, 

 flying into a ship's port with a light in it, although this is by means un- 

 common with flying fish. 



General Remarks. — The extraordinary number of oceanic birds found 

 in the cold regions of the earth, in comparison with the small number 

 found in the tropics, is a very remarkable fact, as it is exactly the re- 

 verse of what we see on land. It can, however, I think, be accounted 

 for as follows : — The higher plants have to deoxidize large quantities 

 of water and carbonic acid for the formation of the sugar, various kinds 

 of oil, camphor, resin, &c, that they secrete ; but this process absorbs 

 an equally large amount of heat and light, which can only be supplied 

 by the sun, consequently they must inhabit warm or temperate cli- 

 mates, and live on land, or at any rate must have the greater portion of 

 their leaves exposed directly to the air ; for water is such a powerful 

 absorbent of heat rays, that a depth of a few inches only is enough to 

 prevent nearly all those that reach the earth on a cloudless day from 

 penetrating further. The lower plants, however, which have little to 

 develope but cellulose and chlorophyll, require less light, and but little 

 heat; they are thus enabled to live under water, and in regions where 

 the more highly organized forms would die, and, being unopposed, they 

 increase here in number and dimensions far more than in warmer lati- 

 tudes or on land ; and as water maintains a more equable temperature 

 than land, it follows that in cold regions the sea supports nearly the 

 whole of the vegetation. This entails an equally large population of 

 the lower marine animals, which subsist on the vegetation, and in their 

 turn supply food to the Petrels, which, carrying about with them in 

 their lungs an apparatus for producing heat, are not under the same ne- 

 cessity as the higher plants of living only in warm climates ; and as 

 the heat in summer is much less in the southern hemisphere than in 

 equal latitudes in the northern, the marine plants, and consequently 

 the Petrels, approach much nearer the Equator in the Antarctic than in 

 the Arctic seas. 



But, although the number of individuals is immense, the species 

 are few, which is, doubtless, owing to the uniformity of the condi- 

 tions under which they live. 



It is very curious to note that most of the species of the Procella- 

 ridm inhabiting the northern hemisphere have " analogues," or closely 

 resembling species, in the southern hemisphere. For instance, the Al- 

 batross of the North Pacific Ocean, D. Brachyura (Temm.), very closely 

 resembles D. exulans (L.), although it is undoubtedly distinct from it. 

 Procellaria glacialis (L.), and Procellaria pacifica (Audub.), again, are 

 nearly related to Procellaria glacialoides (Smith) ; Puffinus cinereus 

 (Gmel.), and Puffinus major (Faber), to Procellaria hcesitata{JAohX.); Puf- 



