358 C. M. Child 



I The Tiirbellariaii Intestine and its Functions 



The names by which the various organs of the lower inverte- 

 brates are designated do not necessarily serve to indicate with 

 any degree of exactness their functions. We commonly speak of 

 the alimentary apparatus of such forms as the turbellaria as an 

 intestine, a digestive system, etc., but strictly speaking the func- 

 tions of this apparatus are not identical in all respects with those 

 of the intestine of the vertebrates for example. It is of course a 

 digestive system, but it is more than that. 



In the first place, the turbellarian intestine undoubtedly serves 

 as a place of storage for undigested nutritive material. Any one 

 who has observed turbellaria feeding can scarcely fail to recognize 

 that this is an important function of the intestine, at least in cer- 

 tain species. Food is often taken until not only the intestine but 

 the whole body is greatly distended. In fact I have often observed 

 the bursting of various species in consequence of rapid intake of 

 food. The opening in such cases is usually small and after out- 

 flow of the excess of material soon closes. Under such conditions 

 the intestinal walls must of course undergo great mechanical 

 extension. 



Secondly, digestion is, at least in part, intracellular and the 

 intestinal cells undoubtedly accumulate reserve material when food 

 is abundant; in otherwords, when digestion proceeds more rapidly 

 than material is removed. 



But besides the functions of digestion and accumulation of 

 reserves the intestine in these forms is the chief means of distri- 

 bution of the nutritive material to various parts of the body, /. e., 

 it is in greater or less degree a circulatory system, a fact which has 

 been recognized by those authors who have termed it the gastro- 

 vascular system. As a gastro-vascular system it contains fluid 

 laden with nutritive substances. This fluid moves to and fro, 

 enters and leaves the various branches and regions according to 

 the muscular contractions of the body-wall. Thus the intestinal 

 wall is subjected to the varying fluid pressures which, however, are 

 more or less typical for each particular region since the muscular 

 contractions are in general typical. A wide range of conditions 



