156 



ROUNDWORMS— THE NEMATHELMINTHES 



tion since they, obviously, are not necessary, but other roundworms that 

 have to do their own digesting do possess them. Egestion, of course, is 

 through the anus. The absorbed food is spread over the body by a fluid 

 in the body cavity around the intestine, so that there is no need for the 

 extensive branching of the intestine as was found in planaria. This 

 serves somewhat as a forerunner to a circulatory system. 



Photo by Winchester 



Fig. 11.2. Ascaris, the large roundworm of man. Note the larger size of the female 

 and the distinct crook at the posterior end of the male. Length of female, 9 inches. 



Respiration is a little difficult to account for, because there would not 

 be oxygen in any quantity in the intestine. Some of the worms that in- 

 habit the small intestine get oxygen by sucking blood into their bodies 

 which contains the oxygen that was absorbed from the person's lungs. 

 Ascaris does not do this with any regularity, so it seems to derive its 

 oxygen in the same manner as the anaerobic bacteria which live without 

 any contact with the air. This is done by an incomplete breaking down 

 of some of their food to produce oxygen necessary for the release of 

 energy from the rest of their food. 



