BINUCLEARITY 51 



nuclei. At certain stages in the life-history the macronucleus disin- 

 tegrates and disappears, while the micronucleus divides into two parts, 

 one of which becomes a new macronucleus. This process of regeneration 

 of the macronucleus occurs most usually in association with the process 

 of conjugation, but may also occur during the course of the ordinary 

 asexual multiplication, when it is known as endomixis. The fact that the 

 macronucleus is formed from one of the products of division of the micro- 

 nucleus is the primary reason why the macronucleus is regarded as 

 a nucleus at all. Furthermore, since the macronucleus disappears during 

 conjugation, and takes no part in the process, it is assumed that the micro- 

 nucleus is essentially the sexual nucleus, and that the macronucleus is 

 vegetative in function, and governs the metabolism and activities of the 

 cell at other times. Though this may be the case, the absolute proof is 

 difficult to obtain. Apart from the fact that it is small in relation to the 

 size of the body, the micronucleus behaves in every way during the whole 

 life of the ciliate as does the nucleus of an organism, such as a flagellate 

 or an amoeba, which possesses no macronucleus. There is little direct 

 evidence that the micronucleus of a ciliate is controlling the metabolism 

 and activities of the cell to a less extent than is the single nucleus of such 

 an organism as an amoeba. 



It is clear that the macronucleus plays an important part in the economy 

 of the cell, and it is equally clear that it is of nuclear origin, but it does 

 not seem clear that because of its existence the functions of the micronucleus 

 are suppressed or supplanted while it is present. The view which main- 

 tains that the micronucleus is purely passive during the asexual life of the 

 organism, and only, so to speak, wakes up to activity during conjugation, 

 while the metabolism of the cell at other times is controlled by the macro- 

 nucleus, has given rise to the conception of two kinds of chromatin, the 

 one sexual or generative in function and the other vegetative. Amongst 

 the Euciliata the two kinds of chromatin are presumed to be separated in 

 different nuclei, while in other cases the same two elements are supposed 

 to coexist in the single nucleus. It is thought that dviring the sexual pro- 

 cess it is the generative chromatin that functions, the vegetative chromatin 

 having been largely got rid of by so-called reduction or maturation pro- 

 cesses. At other times it is the vegetative chromatin which is active, 

 while the generative chromatin, though still present in the nucleus, is 

 passive. 



In this connection it is necessary to recall the fact that in the Mastigo- 

 phora the flagella take origin from a structure called the blepharoplast. ■ In 

 its simplest form this consists of a minute homogeneous granule, which 

 appears to be little more than a thickening of that end of the axoneme 

 which is in the cytoplasm. In certain stages of development of some 



