33 2 SCIENCE PROGRESS. 



of the protoplastic! colonies, and the development of meta- 

 plastid individuals, are in their gross analysis, homologous 

 processes; but when we try to push the comparison between 

 them farther, when we try to ascertain which part of the 

 protoplastid life cycle corresponds to any particular sexual 

 or asexual generation in a metaplastid, it is obvious that 

 without more data to go upon the attempt must fail, be- 

 cause between the acts of conjugation in both cases we 

 have no fixed points from which to reckon. It is, for 

 example, apparently impossible to say at present whether, 

 at some point in the life cycle of a colony of Paramcecia, 

 changes corresponding to the alternation of sexual and 

 asexual generations of the metaplastids pass over all the 

 members of the colony or not. 



For some time, however, it has been known that among 

 the higher plants the change from the sexual to the asexual 

 generation is accompanied by profound changes in the 

 characters of the cells composing them. Indeed, some such 

 state of things might have been anticipated, from the fact 

 that the number of the chromosomes in the nuclei of 

 the cells of any particular species is definite and fixed. 

 And since the act of conjugation consists in the fusion 

 of two nuclei, it follows that this fixed specific number 

 of the chromosomes must be doubled every time that con- 

 jugation occurs, or else the number of the chromosomes 

 characteristic of the species must be periodically halved. 



The latter of these two processes has been found to 

 actually occur, but the manner of its occurrence has been, 

 and still is, matter for the most profound dissent among 

 zoologists and botanists alike. Botanical observers are, 

 however, practically agreed to-day that, in spite of the 

 repeated assertions of Weismann and his pupils to the 

 contrary, the halving of the number of the chromosomes is 

 not brought about by the extrusion of any nuclear elements 

 at all, but occurs during the resting condition of the nuclei, 

 the reduced number of the chromosomes simply appearing 

 in the initial phases of the next division. In unison with 

 this, Boveri found that in certain ovogeneses the number 

 of the chromosomes was neither reduced in the divisions 



