PROTOZOA 



genus found in the soft debris ^at the bottom of clean ponds 

 and ditches, and on the surface of aquatic plants. The shell is 

 chitinoid, and arched on the upper surface, flat on the lower, so 



Fig. 3. — Portion of a Pelomyxa, highly 

 magnified. 



1. Clear external layer of protoplasm, 



ectoplasm. 



2. Central protoplasm, crowded with 



granules, etc. — endoplasm. 



3. Pseudopodia. 



4. Refractive bodies. 



5. Nuclei. 



6. Cylindrical crystals scattered through 



the protoplasm. 



that it is somewhat dome -shaped or hemispherical in form. 

 In the centre of the flat surface is a circular opening through 



Fig. 4. — Arcella vulgaris, Ehr. 



1. Shell. 



2. Protoplasm within the shell. 



3. Protoplasm without the shell— pseudo- 



podia. 



4. Nucleus ; there is more than one. 



5. Contractile vacuole. 



6. Aperture of shell. 



7. Space where the protoplasm has with- 



drawn from shell. 



8. Gas vacuoles. 



which the protoplasm protrudes in the form of blunt pseudopodia. 

 The protoplasm within the shell encloses more than one 

 nucleus, several contractile vacuoles, arranged round the circular 



