360 bulletin: museum of comparative zoology. 



I say " if normal," because the two cleavages (the first and the second) 

 were studied on material fixed by two very different reagents, and it is, 

 therefore, possible that one or other of them represents a distortion of 

 the natural condition. I feel confident that we cannot look upon the 

 dyads in the second cleavage spindle as formed by a confluence of the 

 chromosomes resulting from imperfect fixation, because in the later 

 cleavage stages, fixed by exactly the same method, and even occurring on 

 the same slides, no such confluence is ever seen, although the chromo- 

 somes are very much more crowded. It is, however, altogether possible 

 that the use of strong formalin may result in the mechanical separation 

 of such pairs of chromosomes, if they are not very strongly coherent ; the 

 more so, since its effect on the blastomeres themselves is to shrink and sepa- 

 rate them, rendering their outlines in surface views particularly distinct. 

 On this ground we might assume that in life the chromosomes in the first 

 cleavage spindle, as well as in the second, are dyads and present in only 

 one-half the somatic number ; and that through the action of the fixing 

 reagent the component individuals forming these dyads have been sepa- 

 rated, so that in the preparations the chromosomes appear in the full 

 somatic number. But, of course, to settle the question conclusively will 

 require further research on material treated by other methods. 



V. General Discussion and Conclusions. 



1. The Resting Nucleus. 



The study of the resting nucleus of Gonionemus is of interest chiefly 

 for its bearing on two topics : (1) the general changes taking place during 

 the vegetative period, i. e., between successive divisions ; and (2) the re- 

 lationship existing between the nucleolus and other nuclear structures. 



The first of these I may pass over briefly, since it has recently been re- 

 viewed by Mathews ('98), Crampton ('99), Wilson (:00), and Eohde (:03). 

 But for a clear understanding of the problems in hand a summary of 

 their conclusions may be of value. The occurrence in the nucleus of 

 two classes of bodies distinguished by diametrically opposite reactions 

 toward stains was demonstrated by Heidenhain ('90) and Auerbach ('96). 

 Shortly after, it was shown by the physiologic chemists Lilienfield ('93), 

 Malfalti ('92), and others that this distinction has its basis in the fact that 

 the affinity of chromatin for basic or acid dyes depends upon the degree 

 to which its nucleinic acid is combined with albumin. It remained, 

 however, for Mathews ('98) to correlate these discoveries with the differ- 

 ent staining reactions exhibited by cell structures, and to reach a series 



