1890.] xJib . [Ryder. 



or chromatin proceeds in a way which may be compared to an endogenous 

 or intraplasmic fragmentation of the chromatin substance, part of which 

 is probably not functional as the nucleus, so that even here the germinal 

 matter is " set aside " contrary to the assumption of Weismann, who only 

 finds such a process taking place in Metazoa. These binucleated forms 

 have one macronucleus functional and another sexual micronucleus 

 which is not functional in the ordinary life processes of the species. It is 

 this latter which multiplies and grows at the expense of the cytoplasm of 

 the parent cell, so as to form not only the material for the new micronu- 

 cleus but also that of the new macronucleus, the old macronucleus when 

 exhausted being disintegrated and absorbed by the cytoplasm. In this case 

 the process of conjugation signified a reconstitution of the exhausted 

 macronucleus, a process which always occurs in some forms only when 

 the cytoplasm of the parent is free from unelaborated and non-assimilated 

 constituents. An excess of chromatin and nucleoplasm is produced, part 

 of which becomes the functional nucleus and part is thrust aside as a qui- 

 escent functionless body, the micronucleus. When conjugation occurs it 

 acts as a stimulus, causing the rapid growth and division of the micronu- 

 cleus at the expense of the cytoplasm of both individuals which are not 

 feeding during this process. The reconstitution of the nucleus is there- 

 fore to be interpreted in terms of continuous growth and as a physiologi- 

 cal process which is directly adaptive under the conditions of morphologi- 

 cal differentiation attained by these organisms. The reciprocal fusion of 

 one of the nuclear bodies produced by a subdivision of the micronucleus 

 is to be understood in the way which will be indicated later. 



The death and loss of the power of coordination of movement shown 

 by the cytoplasm of lower unicellular forms, when the nucleus with its 

 chromatin is removed, simply demonstrates the transcendent physiologi- 

 cal importance of the nucleus as a directive centre. This view is also 

 sustained by the fact that ultimate nerve terminations in the Metazoa are 

 lost in some cases within the nucleus. The effects produced by the arti- 

 ficial removal of the nucleus in impairing the power of growth and repro- 

 duction are due to the destruction of the physiological equilibrium between 

 the chromatin and cytoplasm as well as the morphological integrity of 

 the individual. It does not necessarily mean that the nucleus is the repro- 

 ductive agent, but rather tbat this highest end-product of protoplasmic 

 metabolism is the central object for which the investing cytoplasm labors. 

 Neither can, probably, become the centre of reproductive energy or the 

 energy of growth in absolute independence of the other, notwithstanding 

 the fact that there is an apparent absence of the nucleus in Monera, while 

 the cytoplasm is reduced to a minimum in Schizomycetes. 



The conjugation of ciliated Infusoria therefore becomes plainly a pro- 

 cess wherein the nucleus has the usual reproductive function through 

 division of labor coupled with an adaptive arrangement by which a physi- 

 ological substitution of an old for a new nucleus is effected, while the act 

 of conjugation is merely the stimulus through which the active functions 



