VII.] THE BELL-ANIMALCULE. 365 



The various clear spaces {food vacuoles) in 

 it, containing foreign (ingested) bodies (Dia- 

 toms, Protococcus, &c.). 

 S. The contractile vesicle; its position, in the 

 cortical layer just beneath the disc ; its systole 

 and diastole. 



€. The fiucleus ; an elongated curved body in 

 the deeper layer ; sometimes nearly homo- 

 geneous, sometimes more distinctly granular. 

 The nucleus is usually indistinguishable until 

 after treatment with iodine, or acetic acid and 

 magenta (cf. § 5). 



t,. The gullet ; sometimes seen in optical trans- 

 verse section as a clear round space ; some- 

 times seen sideways as a canal opening above 

 into the vestibulum, and ending abruptly be- 

 low in the body-substance. 



17. The a?ius ; look for the egestion of solid par- 

 ticles. 



b. The stalk. 



a. Its length and diameter (measure). 



/3. Its structure; the external homogeneous layer 

 {sheath) continuous with the cuticle; the highly 

 refractive centre {axis or contractile filament) 

 continuous with the cortical layer of the bell. 



2. In the retracted state, 

 a. The body. 



a. Its form; pear-shaped; rounded off above; 

 neither disc nor peristome visible. 



y8. The clear transverse space near the top, indi- 

 cating the interval between the retracted disc 



