SUBJECTS OF NATURAL HISTORY. 199 



the fossil shells which formerly belonged to animals of this descrip- 

 tion, the Ammonite is the most remarkable. Here are several fine 

 specimens of fossil Ammonites : all the connecting calcareous mat- 

 ter has been removed from the septa, and the different chambers 

 have been filled by an infiltrated stony material, with serrated and 

 dovetailed margins. Upon looking at them in this loose detached 

 condition, they look very like vcrtebrse, and they have by some 

 been taken for the vertebral columns of Serpents. The animals to 

 whom these shells belonged are entirely extinct. Although four 

 hundred distinct fossil species are described by naturalists, and 

 more than one hundred of these are met with in our own strata — ■ 

 although they sometimes occur in such abundance that whole rocks 

 are composed of little else — yet not one living individual is now 

 known to exist on the face of the earth. Large specimens of Am- 

 monites are sometimes built into the front of houses, particularly 

 in Somersetshire and Yorkshire, and they are looked upon by the 

 peasantry as petrified Snakes. You are not to conceive that in 

 these enormous remains of the Ammonite you are looking upon the 

 testaceous covering of the animal : this has been entirely removed, 

 and you observe a cast of the interior of the shell only. 



We are now arrived at the inportant division, Vertebrata. The 

 first class is the Fishes ; the next the Amphibia, comprehending 

 Frogs, Toads, &c. This is a deeply interesting family, embracing 

 beings changing, in all their internal machinery, from their aquatic 

 condition, to beings which live and breathe in the atmosphere — 

 undergoing a metamorphosis which affects their osseous, vascular, 

 nervous, and even their digestive systems — changing, in fact, their 

 whole structure. 



Reptilia comprehends the different kinds of Serpents, Crocodiles, 

 Lizards, and Tortoises. These are the last of the cold-blooded ani- 

 mals ; they do not undergo any metamorphosis — a character so pro- 

 minent in the preceding class. ]\Iany of the secondary rocks, espe- 

 cially the Lias Limestones, abound with remains of extraordinaiy 

 and gigantic reptiles, which appear to have abounded in the former 

 seas and estuaries of the globe. 



The next class, Aves, is the first of the hot-blooded animals. 

 Here is a beautiful and interesting department of Natural History : 

 we all derive pleasure from reading an account of any observations 

 <m the liabits, migrations, and plumage of birds ; and you will be 

 gratified to learn that Ornithology is likely soon to boast of an asso- 

 ciation of naturalists who will pay particular attention to every 

 thing relating to it. The London Ornithological Society propose 



