ZOOLOGY. 
INTRODUCTION. 
Definition of Zoology:—That science which treats of liv- 
ing beings is called Biology (ios, life; Adyos, discourse), 
It is divided into Botany, which relates to plants, and Zo- 
ology (aor, animal ; Adyos, discourse), the science treating 
of animals. 
It is difficult to define what an animal is as distinguished 
from a plant, when we consider the simplest forms of either 
kingdom, for it is impossible to draw hard and fast lines in 
nature. In defining the limits between the animal and 
vegetable kingdoms, our ordinary conception of what a 
plant or an animal is will be of little use in dealing with 
the lowest forms of either kingdom. A _ horse, fish, or 
worm differs from an elm tree, a lily, or a fern in having 
organs of sight, of hearing, of smell, of locomotion, and 
special organs of digestion, circulation, and respiration, but 
these plants also take in and absorb food, have a circulation 
of sap, respire through their leaves, and some plants are me- 
chanically sensitive, while others are endowed with motion 
—certain low plants such as diatoms, etc., having this 
power. In plants, the assimilation of food goes on all over 
’ the organism, the transfer of the sap is not confined to any 
one portion or set of organs as such. It is always easy to 
distinguish one of the higher plants from one of the higher 
animals. But when we descend to animals like the sea-ane- 
mones and coral-polyps which were called Zoophytes from 
their general resemblance to flowers, so striking is the’exter- 
nal similarity between the two kinds of organisms that the 
