PARASITES FOUND IN ECHINUS ESCULENTUS, L. 285 



where the last-named passage joins the digestive sac it forms 

 a right angle with the lumen of the alimentary canal. Ante- 

 riorly the digestive sac extends a little way in front of the 

 level of the entrance of the CBSophagus, and when looking 

 through a series of transverse sections it comes into view 

 before any trace of the pharynx makes its appearance. 

 Posteriorly the digestive sac extends to near the end of the 

 body, coming to an end at a distance of perhaps one tenth or 

 one twelfth of the total body-length from the end. 



The digestive sac is lined by a very definite layer which 

 is in the main a plasmodium, though it shows here and there 

 traces of division into cell areas (fig. 6). The limit of the 

 tube is clearly defined, but the basement membrane is very 

 thin, and in places the outer edges of the endoderm plas- 

 modium rests against the packing cells of the body. Inter- 

 nally the lining is produced into many apparently amoeboid 

 processes or pseudopodia, which project loosely into the 

 cavity, and the free ends of which often are cut off and lie as 

 isolated pieces of stained protoplasm in the sections. It is 

 along the inner boundary from which these processes arise 

 that evidence of cell structure is most evident, since the 

 chinks between the bases of the pseudopodia are continued 

 by fine lines, which pass a little way into plasmodiuni, 

 dividing it as it were into cell areas. 



TMiroughout the plasmodium deeply staining nuclei are 

 distributed, and numerous vacuoles are scattered ; some 

 apparently contain drops of fluid, probably oil or fat ; others 

 contain uniformly staining spheres of unknown nature, 



I have not been able to find any trace of a secretory 

 apparatus; neither canals nor pore could be made out in any 

 of my sections. 



Nervous System. — The nervous system consists of a 

 well-marked ganglion, situated just anterior to the mouth; it 

 is somewhat rectangular in outline, and a nerve is given off 

 from each angle. The anterior pair of nerves soon disappear; 

 the posterior, which bend backwards, are stained, but I failed 

 to follow them very far down the body. In one, stained 



