268 PARAMCECIUM chap. 



glass, it frequently assumes a remarkable appearance. Long 

 delicate threads suddenly appear, projecting from its surface 

 in all directions (c) and looking very much as if the cilia had 

 suddenly protruded to many times their original length. But 

 these filaments have really _ nothing to do with the cilia ; they 

 are contained under ordinary circumstances in the trichocysts, 

 probably coiled up; and by the contraction of the cortex 

 consequent upon any sudden irritation they are projected in 

 the way indicated. In Fig. 70 b, a few trichocysts (trch) are 

 shown in the exploded condition, i.e., with the threads pro- 

 truded. Most likely these bodies are weapons of offence like 

 the very similar, structures (nematocysts)" found in polypes 

 (seep. 29s, Fig. 75). 



Paramoecium multiplies by simple fission, the division of 

 the body being always preceded by the elongation and 

 subsequent division of the^ mega- and microriucleus 

 (Fig. 70, d). 



Conjugation (p. 237) also occurs, usually after multi- 

 plication by fission has gone on for some time. Two Para- 

 moecia come into contact by their ventral faces, and in each 

 of "these conjugating individuals or gametes the meganucleus 

 and micronucleus undergo a somewhat complicated series of 

 changes, the essential' part of the process being the fusion of 

 two products of the division of the micronuclei, one from 

 each gamete, each of which then contains a single nuclear 

 body, the conjugation-nucleus, formed by the union of nuclear 

 matter derived from two distinct individuals, and therefore 

 comparable to the nucleus of the oosperm in the higher 

 animals (p. 197). In this oase, however, the two entire 

 gametes do not unite into one, but separate after the process 

 is complete and begin once more to lead an independent exist- 

 ence, when once more ordinary transverse fission takes place. 



