DUFEEEXCES BETWEEN ANIMALS AND PLANTS. 25 



simple, and their nerves are, in general, parallel : their flowers 

 possess only three stamens, r their multiples (6 or 9), and 

 they are often incomplete in many of their parts. None of 

 these endogenous vegetables grow by layers, but by a swelling 

 out of their internal structure, just as the horny or calca- 

 reous envelope of insects and Crustacea is periodically shed 

 to allow of a general increase from within. Among some 

 classes and families of both kingdoms there are many groups 

 which are aquatic in then* habits. 



[ 73. The third great division of the animal kingdom, called 

 vertebrata, comprehends all those animals provided with two 

 distinct nervous systems ; the one formed of a series of gan- 

 glia extending through the body, and called the ganglionic 

 or sympathetic system, which presides over the functions of 

 internal life or nutrition. The other, consecrated to exter- 

 nal life or relation, is composed of the brain, spinal cord, 

 and nerves, the principal centres of which are enclosed in 

 the cranium and the canal of the vertebral column ; they 

 all possess an internal framework or skeleton, the several 

 jointed pieces of which are moveable on each other. The 

 most perfect possess five senses ; four of these occupying the 

 cavity of the cranium, and there are never more than four 

 members disposed in pairs. They have all a heart with red 

 blood, and respire by lungs, or branchiae, and the sexes are 

 separate. They are usually parted into two great groups, the 

 vertebrata with cold blood and feeble respiration, fishes 

 and reptiles, and the vertebrata with warm blood and a com- 

 plete respiration, birds and mammals. The nervous system, 

 in this division of the series, attains its greatest development, 

 presenting the most perfect centralisation, from which the most 

 noble faculties emanate. 



[ 74. We compare with this group of animals the dicotyle- 

 donous vegetables, or those whose embryo possesses two coty- 

 ledons or seed lobes. The form of their reproductive organs 

 is always the most perfect, being composed of the number 

 five and its multiples. Their trunks or stems grow by the 

 addition of concentric layers or rings of wood made to their 

 outer surface. Being thus exogenous, they display more or 

 less solidity internally, like the osseous skeleton of the verte- 

 brata. The central marrow or pith is enclosed in a sheath 

 (analagous to the spinal canal) extending through the entire 



