SUBJECTS OF NATURAL HISTORY. 193 



Geology or Mineralogy. — Zoology embraces the whole animal 

 kingdom ; and, looking to the organization of every species, it is 

 naturally divided into four great divisions. The first division (Ver- 

 tebrata) includes all those animals which have a vertebral column 

 or spine, supporting an internal bony skeleton. The second (Mol- 

 lusca) have no internal bony structure ; on the contrary, they are 

 clothed externally with a shell or dense tunic, and are chiefly inha- 

 bitants of the ocean. The third division ( Articulata J , so called be- 

 cause the different portions of their body are composed of moveable 

 pieces articulated to each other, differ from MoUusca in generally 

 possessing a skeleton, and from Vertebrata by the skeleton being ex- 

 ternal, and not internal. The fourth division (Radiala) differ from 

 the three preceding in the greater simplicity of their structure, 

 and in the almost total absence of any thing like a nervous sys- 

 tem. 



Botany embraces the whole of the vegetable kingdom ; and refer- 

 ring to the organization of every species, it is naturally divided into 

 two great divisions, Vascidares and Celltilares. Vasculares have a 

 vascular and cellular structure, with delicate spiral vessels in their 

 tissue ; they have a sexual apparatus, and are propagated by seed. 

 Cellulares have a cellular structure only, are destitute of spiral ves- 

 sels, without any sexual apparatus, and the plants included are not 

 propagated by seeds. If we proceed to investigate the structure of 

 the great division Vasculares, it is found distinguished, by a truly na- 

 tural character, into two sub-divisions; the one including plants 

 which grow by the addition of new matter on the outside of the old 

 (Exogense), and the other those which grow by the addition of new 

 matter in the centre of the old ( Endogenae ) . Exogenous plants 

 have a structure composed of a central pith, an external cellular or 

 fibrous ring or bark, and an intermediate woody mass, well-illus- 

 trated in a young shoot of Elder. Endogenous plants, on the other 

 hand, have neither bark, nor pith, nor wood, but are made up of 

 tubes and fibres imbedded in cellular substance, as in the Palm, the 

 Cane, and Bamboo. Again, in Exogenx the seed is dicotyledonous, 

 and the veins of the leaf are variously netted; in Endogenw it is vw- 

 nocolyledonous, and the veins of the leaf are parallel. It is thus we 

 look to structure and physiology for the first lines of a natural me- 

 thod of classification, both in animals and plants ; and you will find 

 all the standard works upon Natural History which have been late- 

 ly published adopting these views. 



I now refer you to the following classification of tlic several 

 tribes of animals; and, commencing with the simplest forms, shall 



