26 THE INDIVIDUAL ORGANISM 



6. The circulatory system, a common carrier system of pumps, pipe 

 lines, and loading platforms that connects and keeps coordinate 

 the other systems of the body and has accessory but very important 

 functions of protection against invasion by parasitic organisms. 



7. The nervous system, which receives sensory stimuli from the out- 

 side world and from other body regions and functions as a special 

 coordinating system between the various body parts and between 

 the body and the outside world. 



8. The endocrine system, a complex of widely separated glands of 

 internal secretion that provide an important accessory control over 

 body coordination. 



9. The reproductive systems, male and female in separate bodies, the 

 organs containing the reproductive cells (ovaries or testes) and 

 various supplementary organs, structurally combined (especially 

 in the male) with the excretory system, the two frequently grouped 

 together as the urinogenital system. 



None of these systems is complete in itself. Each is a specialized func- 

 tional division of a highly integrated single individual. Their segregation 

 is very useful for analysis, but no system can be wholly understood unless 

 it is recognized as but one dependent part of a whole. 



