268 PARAMCECIUM CHAP. 



times their original length. But these filaments have 

 really nothing to do with the cilia ; they are contained 

 under ordinary circumstances in the trichocysts, pro- 

 bably 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 

 (trek) are shown in the exploded condition, i.e., with the 

 threads protruded. Most likely these bodies are weapons 

 of offence like the very similar structures (nematocysts) 

 found in polypes (see Chapter V., Fig. 77). 



Paramoecium multiplies by simple fission, the division 

 of the body being always preceded by the elongation 

 and subsequent division of the mega- and micro-nucleus, 

 accompanied by the regeneration of the parts wanting in 

 each product (Fig. 71, D). 



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

 multiplication by fission has gone on for some time. 

 Two Paramcecia come into contact by their ventral faces, 

 and in each of these conjugating individuals or gametes 

 the meganucleus takes no part in the process and de- 

 generates, while the micronucleus undergoes 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). 

 The other products of division of the micronucleus 

 disappear (compare Chapter XII., p. 572), and a new 

 mega- and micro-nucleus arise from the conjugation- 

 nucleus. In this case, however, the two entire gametes 

 do not unite to form a zygote, but separate after the 

 process is complete and begin once more to lead an 



