462 



APPENDIX 



permanent pool contains these forms in abundance. Ameba readily 

 persists year after year in aquaria where fish are present, although they 

 disappear at times temporarily. 



Expt. 5. The fifth specimen is a remarkable ciliated infusor named 

 Vorticella. We have already probably seen early stages in the develop- 

 ment of this animal as small spherical transparent masses of protoplasm 

 rolling about through the drops of water on the previous slides. A 

 later stage- shows a circular fringe of cilia developed on one side of these 

 spherules and a pointed short projection on the opposite side of the 

 animal. A still later stage shows animals with this process developed 

 into a long contractile filament, the muscle-stem of this unicell, which 



FIG. 255 



Vorticella, showing various phases and the modes of reproduction: (1) N, macronucleus; n, 

 micronucleus; cv, contractile vacuole; fv, food vacuole; m, gullet; v, vestibule; (2) an encysted 

 phase, with 3, its mode of division; 4, a free-swimming unit dividing off; 5, formation of sev- 

 eral small units (mg); 6, conjugation of a small zooid (mg) with one of .larger size. (Bvitschli.) 



the Vorticella drags behind him as he rapidly sucks his way through the 

 water by means of the cilia at the vortex. Soon a sort of hook develops 

 at the end of this filament and catches upon some mass of vegetal matter 

 and thus anchors the animal for the rest of its life of a few days. Draw 

 all these forms. See also if possible the colony-form, Zoothamniwn. 



Observe in the anchored variety of Vorticella (1) the vortex of water 

 (and contained food) passing into the animal; (2) the internal organs; 

 (3) the very quick spiral contraction of the stem-muscle when the animal 

 is jarred or otherwise stimulated ; (4) the gradual probably passive 

 extension of the animal on the end of the uncoiling stem; and (5) that 

 the muscle soon becomes fatigued and fails to respond to stimulation. 



