222 CORA J. BECKWITH 



2. Maturation stages 



The maturation phenomena take place while the egg is still in 

 the gonophore as Smallwood ('09) states, and not after leaving it 

 (Bunting '94). The lightly staining, homogeneous condition of 

 the nucleus, which has long been recognized as a characteristic 

 of the hydroid egg, and which has led to much confusion concern- 

 ing the maturation stages, persists until the nucleus breaks down 

 to form the chromosomes. The first indication of reappearing 

 chromosomes occurs in gonophores killed from 20 to 30 minutes 

 before eggs from the same colony are deposited. Since the refor- 

 mation of the chromosomes is best seen in material preserved in 

 fluids which do not cause a heavy precipitate, the following de- 

 scription is based on material fixed either in Meves' or Flem- 

 ming's fluid, neutral formalin, or hot water. The deeply staining 

 nucleolus is usually still present at the inner border of the nucleus ; 

 its history will be described more fully later. 



Out of the apparently homogeneous ground-substance of the 

 resting nucleus, there appear very lightly staining threads on 

 which are groups of granules staining a little more intensely than 

 the threads. These threads appear in pairs, either parallel or 

 X like in form (figs. 30, 31). In either case many fine branches 

 merge from the main threads into the general homogeneous 

 ground-substance. The number of these groups of threads in a 

 single nucleus corresponds to the haploid number of chromosomes 

 (12 or 14). The exact haploid number has not been determined 

 but since 14 such pairs of threads is the number most frequently 

 found in a nucleus and since 14 tetrads is the usual number found 

 in the later stages (figs. 4, 46), it seems certain that this repre- 

 sents the haploid number and that they are bivalent chromosomes. 

 The chromosomes now condense rapidly into tetrads which are 

 very much smaller than the crosses. The initial stage in this 

 process consists in a shorting of the arms of the X and the collec- 

 tion of the granules in a mass at the center, the latter taking a 

 slightly deeper stain than before (fig. 32). In a later stage (fig. 

 33) the ends of the arms of the X are still visible, although the 

 bulk of the granules appear at the center. The condensation 



