342 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



ure 122 shows three or four such segments, while the remainder of the 

 reticulum still preserves the more primitive condition. Tims the condi- 

 tion of the nucleus as a whole is now similar to that of somatic cells 

 and oogonia at a corresponding stage. As this process of condensation of 

 the separate chromatic masses, together with the gradual disintegration 

 of the nucleolar shell continues, the segments of this kind increase in 

 number, until at last a stage is reached where they constitute all the 

 strands of the net (Fig. 123), being quite sharply separated from one 

 another, although still connected by persisting linin strands. It is 

 now clearly seen that the chromatin shell of the nucleolus (Fig. 123) 

 has separated into a variable number of separate chromatin masses, 

 which probably migrate outward along the linin strands. The final 

 I'esult of the process is that all the chromatin is collected into the 

 "beaded" segments (Figs. 125-127), leaving the nucleus otherwise 

 entirely empty except for the connecting achromatic threads and the 

 central portion of the nucleolus, a sharply outlined, strongly staining 

 spherical structure, which pei-sists after the disintegration of the nucle- 

 olar shell. 



"While this series of changes has been taking place, the cytoplasmic 

 body of the cell has dwindled, and during the remainder of this phase 

 of nuclear activity is very distinctly smaller than in the preceding "rest- 

 ing " stage, a condition similar to that already described in the case of the 

 first generation of spermatocytes (see page 314), and one which points 

 to the great metabolic activity of the nuclear structures. 



Since it is at a corresponding phase in the maturation division of the 

 male germ cells that contraction phases so commonly occur, it is of in- 

 terest to observe that here, too, such appearances are occasionally seen, 

 but only rarely, and then never in an extreme condition. In the later 

 " segment stage " they are never seen, probably because of the stoutness 

 of the chromatic segments themselves. 



The cells now present a very characteristic appearance (Figs. 125- 

 127), and owing to their comparatively large size, allow on isolated 

 specimens a very accurate mapping of their nuclear contents. Fortu- 

 nately, with material preserved in Flemming's fluid, the female gonads 

 lend themselves quite as readily to the making of isolation preparations 

 as do the male gonads, so that I have been able to study a considerable 

 number (over one hundred) of entire nuclei at this stage. From sec- 

 tions the nuclear conditions are very much less easily resolved, since the 

 section plane frequently cuts the chromatic segments, and reconstruction 

 of these from adjacent sections is accompanied by much difficulty and 



