6 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



food ball, and is filled with water which has been swal- 

 lowed with the food. The ball of food, with its .surround- 

 ing water, is a food vacuole (Fig. 1, g). After a time 

 the water disappears, and a number of food balls, without 

 the layer of water, are usually present (Fig. 1, //) . Some- 

 times the endosarc contains drops of water without food 

 matter. 



b. Occasionally the endosarc contains the entire bodies 

 of small organisms, such as rotifera, alga,', etc., which have 

 been swallowed as food. 



c. Occasionally the endosarc contains other foreign 

 bodies, such as grains of sand, particles of sawdust, etc. 



d. If possible, watch the process of ingest ion of food 

 matter, the formation of a food vacuole, and the expulsion 

 of indigestible matter from the body. Notice that food 

 may pass in or be expelled at any point on the surface. 



VI. Structural constituents of the endosarc : 



a. In some specimens the endosarc will be found to 

 contain a discoidal or spherical transparent body, the endo- 

 plast or nucleus (Fig. 1, i). It does not change its form 

 with the movements of the body, and it usually lies near 

 the posterior end when the organism is progressing. It 

 may be surrounded by an area of non-granular endosarc. 



b. In some specimens a clear, transparent, liquid globule, 

 the contractile vesicle (Fig. 1, A-), may be found, usually 

 behind the nucleus. If carefully watched, it will be seen 

 to gradually enlarge for several seconds and then suddenly 

 collapse and disappear, to reappear again in a few seconds 

 at the same or nearly the same place. 



c. The endosarc usually contains other bodies, such as 

 crystals, large granules, and drops of oil. 



VII. Make sketches showing as many of these points 

 as possible. 



