FUNCTIONS AND SYSTEMS. 



123 



ity (COB). The inner tube is the alimentary canal, opening in 

 front by the mouth and behind by the anus; the outer tube is 

 the body- wall, and its cavity is the J)ody-ca/vity or ccd-oin. The 

 ccelom is not, however, a free continuous space extending from 

 end to end, but is divided transversely by a series of thin muscular 

 partitions, the dissepiments, into a series of closed chambers trav- 

 ersed by the alimentary canal. Each compartment corresponds 

 to one somite, the dissepiments being opposite the external fur- 

 rows mentioned on p. 120. All the organs of the body are origi- 

 nally developed from the walls of these chambers, and some of 

 them (e.g., the organs of excretion ) project into the cavities of 

 the chambers, that is, into the coelom. 



Organs and Systems. The apparatus or organs by which the 

 worm lives and makes exchanges with its environment are widely 

 different from those of the fern ; and since they are more com- 

 plex, and from a mechanical point of view more perfect, the ani- 

 mal is said to be more highly organised. In the fern certain tis- 

 sues were found to be constantly associated in definite groups or 

 systems (fundamental, epidermal, and fibro- vascular systems, p. 72). 

 In Lumbricus like associations or systems exist, each consisting of 

 a number of different organs which co-operate to perform some 

 important function, such as alimentation, circulation, reproduc- 

 tion, etc. 



Such groups of co-operative organs are known as organic sys- 

 tems, and they take their special names from the leading func- 

 tions alimentation, respiration, excretion, etc. which they re- 

 spectively perform. They are shown in the following table :- 



ANIMAL FUNCTIONS AND SYSTEMS or ORGANS. 



a. Alimentary. 



b. Circulatory. 



c. Metabolic. 

 (I. Excretory. 

 e. Respiratory. 

 /. Motor. 



g. Co-ordinative. 



Ti. Sensitive. 



i. Supporting, Connecting, 



Protecting, etc. 



j. Reproductive. 



Nutrition. 



L 



Relation. 



FOR THE INDIVIDUAL. 



} FOR THE RACE. 



