THE CONSERVATION OF LIFE 



223 



by the fact that it never takes in particles of food. The cortical 

 layer is specially marked as the seat of the ' trichocysts,' minute 

 organs of defence which may be compared to the familiar poison- 

 cells of the corals, sea-anemones, and jelly-fishes. 



The trichocysts are small, spindle-shaped formations, filled 

 with a watery fluid. Touch or other stimuli of a mechanical 

 or chemical nature void them. When brought in contact with 

 water the contents congeal into a thin, hard thread which 

 eventually bores into the body of the attacker or prey, and. there 

 probably causes a burning pain or paralysis. I say, probably, 

 because no satisfactory observation has so far been recorded. 



The alveolate layer, which I mentioned before, is partly trans- 

 formed into contractile fibrils, a kind of primitive muscle surround- 

 ing the body longitudinally, thus imparting to it great motility. 



As regards the 

 nuclear apparatus 

 of the Ciliates, we 

 find in this class 

 two different kinds 

 of nucleus, the so- 

 called macro-nuc- 

 leus, which is often 

 distinguished by a 

 very considerable 

 size, and the micro- 

 nucleus. While 

 the macro-nucleus 

 controls and regu- 

 lates all ' vegetal 



functions ' of cell-life digestion, respiration, locomotion, etc., 

 the micro-nucleus becomes active only at times of sexual 

 reproduction. The changes which it then undergoes are so 

 striking that it has been described as the sex-nucleus. 



Like Amoebae, the Ciliates reproduce by simple fission, but 

 while in the Amoebae the two daughter-individuals are at once 

 equivalent it is not so here, owing to the great differentiation of 

 the body. Let us observe, as an example, a trumpet-animalcule 

 (fig. 54). 



The anterior end, which has been enlarged like a trumpet, 



FIG. 54. TRUMPET-ANIMALCULE (StentOT CCerilleUS) IN 

 THREE SUCCESSIVE STAGES OF DIVISION. 



