CONSTITUTION OF THE ANIMAL AND PLANT KINGDOMS. 43 



particular impress on coins of the country or territory from which 

 they were issued. 



Yet another illustration may be given of the constitution of 

 animal types by way of impressing their distinctive character on the 

 mind. If we bisect the body of a fish by splitting it through the 

 spine from head to tail, we discover a highly characteristic disposition 



FIG. 5. SECTION OF VERTEBRATE. 



Diagrammatic plan of Vertebrate type, a a a, vertebral column or spine, the 

 upper arches of which enclose the brain and spinal cord; bbb, "cerebro- 

 spinal " nervous system or axis, consisting of the brain and spinal cord ; 

 cc, digestive or alimentary system; d, anus; e, \\eart\fff, "sympathetic" 

 or "ganglionic" nervous system. * 



of its organs and parts. Lying along the back, and enclosed within 

 the skull and spine (Fig. 5, a a) as within a tube, we find the 

 nervous system (b b). consisting of brain and spinal cord. Lowest 

 down, and lying on the floor of the body, is the heart (e) above the 

 heart and in the middle position is the digestive system (<r) ; and 

 above this system in turn is a 

 second nervous system, dis- 

 tinct from the brain and spinal 

 cord, and known as the sym- 

 pathetic system (//). Thus 

 the positions of organs in the 

 fish, with the exception of the 

 digestive system, are exactly 

 reversed from those of the 

 lobster and butterfly; whilst 

 in that its chief nervous system 

 (b, b) is enclosed within the 

 bony tube formed by skull and spine (a, a\ the fish presents a most 

 material difference from both animals. Furthermore, we should find 

 that the "fins" of the fish which represent the limbs of higher 

 animals are never more than four in number, and that they are 

 disposed in pairs. A simple diagram, then, might be constructed of 

 the fish (Fig. 5), showing the positions of the various systems as just 

 narrated, whilst a similar idea of vertebrate structure is afforded by 

 the cross-section in Fig. i, A ; and such a diagram would hold true 



FIG. 6. DIAGRAM OF MOLLUSC. 



