232 GEOLOGICAL BIOLOGY. 



parts, i.e., the specialization of functions, along the digestive 

 tract. In such an organism as the lobster, for instance, we 

 find a definite arrangement of specialized functions with dif- 

 ferentiated organs, distributed along the line of the axis from 

 the antennae to the extreme posterior end of the body. 



Differentiation Along the Digestive Tract. — Without con- 

 sidering the skeletal parts, but looking at the organism in re- 

 spect to its digestive tract alone, we find the following series 

 of differentiated parts: 



First, the detection of food. Provision for this is made by 

 special organs of sense, antennae, eyes, organs of smell and 

 of taste, and, finally, those of hearing. 



Second, the prehension of food. For this purpose jaws and 

 teeth and other apparatus are provided. 



Third, the breaking or gross reduction of food ior diges- 

 tion. For this purpose the teeth and jaws are brought into 

 action. 



Fourth, the digestion of food. In this process several spe- 

 cial organs take part, the most important of which are the 

 stomach and the secretions which are furnished at that point 

 in the enteron ; but there are, in addition, in higher organ- 

 isms, numerous specialized glands, secreting digestive fluids 

 with differing properties. 



Fifth, the absorption of food. For this function the intes- 

 tine and associated organs are differentiated. 



Sixth, the distribution and application of food-products. 

 To this group of functions are applied the organs of circula- 

 tion, and auxiliary to them are those of respiration, and the 

 corresponding organs. 



Seventh, elimination of effete matter. The organs for 

 this function are at the anal termination of the enteron, and 

 auxiliary organs are found associated with the circulatory sys- 

 tem, as, in the higher animals, renal organs; and even the 

 skin subserves the same function, in part, in perspiration. 



Differentiation of the Motory System into Muscular and Skeletal 

 Organs. — This principle of differentiation might be traced in 

 relation to the skeletal framework of the body ; but these 

 relations are not fundamental, and the organs are adjusted to 

 them to conserve convenience and compactness of arrangement. 



