268 PARAMCECIUM CHAP. 



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. 71, B, a few trichocysts (trcK) 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 

 (see Chapter V., Fig. 77). 



Paramcecium multiplies by simple fission, the division of 

 the body being always preceded by the elongation and 

 subsequent division of the mega- and micronucleus 

 (Fig. 71, D). 



Conjugation (pp. 237, 251) also occurs, usually after multi- 

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

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

 of these conjugating individuals or gametes the meganucleus 

 degenerates, and the micronucleus undergoes a somewhat, 

 complicated series of changes, the essential part of the pro- 

 cess being the fusion of two products of the division of the 

 micronuclei, one from each gamete, each of which then con- 

 tains 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) : the other products 

 of division of the micro-nucleus disappear, and a new mega- 

 and micro-nucleus arise from the conjugation-nucleus. In 

 this case, 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 existence, when ordinary 

 transverse fission again takes place, 



