13° 



MANUAL OF ELEMENTARY ZOOLOGY 



wards and driving the blunt end of the animal forwards, 



with a rotating movement like that of a rifle bullet owing 



to its spiral shape. 



Like Amoeba, Paramecium is non-cellular. There is 

 a soft, granular endoplasm, and an ectoplasm 

 which is much firmer than that of Amxba and 

 gives the body its shape, but is elastic, so 

 that the animal can bend and squeeze through 



narrow openings. The outermost layer of the ectoplasm is 



Eotoplasm 



and 



Endoplasm, 



f.v. 



Fig. 79- — Paramecium caudatum. 



A, An individual seen from the left side, highly magnified ; B, a diagrammatic 



view of an individual from the ventral side, less highly magnified. 



an., Position of temporary anus ; c.v., contractile vacuole ; ec. t ectoplasm with 

 trichocysts; j.v., food vacuoles ; g., gullet; meg., meganucleus; mi., micro- 

 nucleus ; /*.;//., undulating memhrane ; v., vestibule. 



a tough pellicle. Whether an "alveolar layer" (p. 114) 

 underlies it, or is included in it, is uncertain. Below 

 the pellicle comes the cortex, a thicker, clear layer of ecto- 

 plasm in which are embedded peculiar structures known 

 as trichocysts. These are spindle-shaped bodies with a 

 sharp point, and consist of some denser substance than 

 the protoplasm. They are placed at right angles to the 

 surface, with the point outwards. If the animal be strongly 

 stimulated, as by a solution of some irritating substance, 

 they suddenly elongate into threads and project from the 

 body. The pointed end is harder than the rest and 



