10 THE DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



are known as sensory fibres. In most cases the sensory nerves 

 are united at their peripheral end with the so-called "end- 

 organs " in the skin, &c., these end-organs being derived from 

 the modified epithelial cells. 



Such are some of the modifications that are assumed by cells 

 in the animal kingdom. 



The lowest animals, we shall see, possess neither tissues nor 

 organs composed of cells, and yet each organism, although only 

 a single cell, is complete in itself and reproduces a similar 

 species. 



The Difpeebncbs bktwebn Animals and Plants. 



Living bodies are divided into two groups called " king- 

 doms," the one the Animal Kingdom, the other the Vegetable 

 Kingdom. Although there are apparently great differences be- 

 tween the two, yet when we come to examine the lowest animal 

 forms and compare them with the lowest vegetal forms we 

 shall observe so great a similarity that it is impossible to say to 

 which kingdom they belong. In fact, there is no hard-and-fast 

 line to be drawn between these two organic groups. Such 

 lowly creatures as Plasmodium and Volvox are treated by 

 botanists as plants, whilst the zoologist includes them in the 

 Protozoa.^ It may be said, speaking generally, that animals 

 are capable of free movement and that plants are fixed ; but 

 when we examine some of the simplest forms of life this 

 distinction will be found untenable. Animals are endowed with 

 sensation, plants are not, as a rule ; but such plants as Drosera, 

 Venus' 8 flij-trap, &c., surely have this phenomenon developed. 

 Animals have their organs internal, their absorbent surface 

 inside ; plants have external organs, and the absorbent surface 

 also external. Yet the Tapeworms {Qe,<1oda) obtain their 

 nourishment by osmosis through the skin. 



When we compare the tissues of an animal with the tissues 

 of a plant, then we observe greater diff'erences. The cells 



' 'A Sy.stem of Medicine,' vol. ii. Pt. ii., article by E. A. Miiichiu — 

 " Protozoa," p. 17. 1907. 



