PARAMECIUM 



131 



A.i>. ........ 



remains unaltered as a spear-point. The trichocysts are 

 supposed to be offensive or defensive weapons, but it has 

 never been shown that this is the case. The pellicle is 

 marked by rows of hexagonal pits, in the midst of each 

 of which a cilium arises, while the trichocysts lie under 

 the ridges which separate the pits. Each cilium consists 

 of an axial thread and a covering layer continuous with 

 the pellicle. The axial thread stops short of the tip of 

 the cilium, which is pointed. Below the cilium the thread 



is continued inwards 

 into the cortex, at the 

 inner limit of which 

 it bears a swelling 

 known as the basal 

 granule. The endo- 

 plasm contains 

 numerous granules, 

 some of which appear 

 to consist of waste 

 matters ready for ex- 

 cretion, while others 

 may be stored nutri- 

 ment. Glycogen is 

 diffused through the 

 endoplasm. 

 Paramecium cauda- 

 tum has 

 two nu- 

 clei. These, however, 

 are not both of the 

 same kind, like the nuclei of a Pelomyxa (p. 119), but con- 

 sist of portions of the nucleoplasm specialised for different 

 purposes. One is large and is concerned with the ordinary 

 life of the body. This is known as the meganucleus. The 

 other is small and is specialised for the purpose of con- 

 jugation. This is the micronucleus. 1 We may roughly 

 compare the meganucleus with the nuclei of the body-cells 

 of the frog and the micronucleus with the nuclei of the 

 germs. The nuclei lie in the endoplasm above the gullet, 

 the micronucleus in a cleft in the side of the meganucleus. 

 1 The species known as Paramecium aurelia has two micronuclei. 



t>.g. 



Fig. 80. — A portion of the surface of 

 Paramecium, very highly magnified. 

 — Partly after Biitschli. 



b.g., Basal granule of a cilium; «., cilium; h.p., 

 hexagonal pits ; tri., trichocysts. 



Nuclei. 



