RELATION OF BURSARIA TO FOOD 7 



Figure 1, //, is a sagittal section through the body in the plane 

 indicated by the straight line through figure 1, /; it shows the 

 path of total rejection, arrows A, the path of entrance (by heavy 

 arrows D) and the path of rejection of smaller particles (by 

 arrows C). 



At the point of entrance into the endoplasm the transport of 

 the accepted particles is brought about not alone by the cilia 

 but also if not exclusively, in the case of larger particles, by a 

 peristaltic wave in the wall of the oral cavity behind the par- 

 ticle pushing it into the body. 



FORMATION OF THE VACUOLE AND THE ELIMINATION OF RESIDUES 



The vacuoles when formed always contain some liquid, though 

 at times the amount may be very small. The size and shape 

 of the vacuoles varies greatly and depends upon the kind of 

 food eaten, and upon many other conditions, as will be shown. 

 Often the food forms large irregular masses, which in the case of 

 fresh yolk may so completely fill the body that after a half- 

 hour or more of feeding the dorsal side of the body cortex is 

 burst open and the food mass is extruded. The opening then 

 closes and the organism again assumes its usual shape. The 

 rate of formation of the vacuoles is intimately bound up with 

 the same complex conditions which determine their size and 

 shape. The circulation of the vacuoles in Bursaria is not re- 

 ducible to any definite order, such as has been shown to exist 

 more or less definiteh^ in Paramecium, by Metalnikow ('12) and 

 others, and in Carchesium by Greenwood ('94). The vacuoles 

 often become lodged in one place and there digestion is com- 

 pleted. This may often be seen in cases where fat-extracted 

 3^olk particles become lodged in the tail. During digestion and 

 resorption the large vacuoles usually become smaller and any 

 residual contents are finally extruded. The residues are always 

 extruded from a small area on the mid-dorsal side of the body 

 of the organism. This may readily be demonstrated by feeding 

 the animals Chinese ink. The changes which take place in the 

 food vacuole from its formation to its disappearance will be 

 considered in detail in a later paper. 



