ALIMENTARY SYSTEM. 15 
individuality of each unit, for the tailor soon loses the art 
of making weapons, and wice versa. The greater the extent 
to which the division of labour is carried the more pro- 
nounced will be the individuality of the community. Ina 
similar manner it will be seen that the lower animal types 
with little physiological division of labour have little in- 
dividuality and portions of them can survive when separated 
from the parent, but the higher types have pronounced in- 
dividuality and death ensues upon the disturbance of a 
finely-balanced equilibrium of the parts. 
1. The Alimentary System is perhaps the most 
fundamental; the parts of which may be divided into :— 
(1) INcEsTIvE SystEM.—The ingestive organs are those 
connected with the seizure of food and its introduction into 
the body. As the essential purpose of locomotion is the 
obtaining of food they are closely allied to motor organs and 
are often modified from them. The ingestive aperture is the 
mouth, usually surrounded by organs for seizing or preparing 
the food, ¢.g., jaws, teeth, tentacles, &c. 
(2) DicestivE SystEM.—Digestive organs are more 
directly concerned with the reduction of food into a soluble 
and diffusible condition, There is usually a cavity, the 
enteron or gastric cavity, in which digestion is effected, and 
there are often digestive glands which secrete a digestive 
fluid. This cavity is part of the a/mentary canal, occupying 
the interior of the animal and opening to the exterior by the 
mouth, or by mouth and anus. 
(3) EcrstivE SystemM.—Egestive organs are concerned 
with the removal of waste residue of the food. The egestive 
aperture when present is called the azus; in higher types 
it is usually at the posterior end of the body. 
2. Motor System.—lIna motor system the property of 
contractility is especially concentrated. The primary object 
of movement is the obtaining of food, and in the case of 
sedentary (fixed) animals the motor organs are employed, not 
to move the animal to its food, but the food to the animal. 
The two principal organs of movement are :— 
(r) Cita AND FLacELLa.—These are vibratile processes 
of protoplasm which, by striking the water or surrounding 
fluid medium, cause either motion of the medium or that of 
