158 CHAS. W. METZ AND JOSE F. XOXIDEZ. 



In number 2056 the nucleolus is prominent from the beginning 

 of the growth period. It grows gradually and serves as an addi- 

 tional criterion for seriating the growth stages. When the 

 nucleus begins to become irregular in outline, the nucleolus elong- 

 ates and becomes bilobed, then double. One portion is large, 

 dense and irregularly shaped; the other is smaller, less dense and 

 nearly spherical resembling chromatin in texture. The two 

 parts are often connected by a dark, thin thread. In the late 

 growth stages the large, irregular portion frequently lies near the 

 periphery of the cell, suggesting that it may be cast off. We 

 have not been able to determine its fate, on account of the scarcity 

 of prophase figures, but it seems to disappear before the chromo- 

 somes go on the spindle. The smaller portion appears on the 

 spindle in its characteristic spherical form, but reduced in size, and 

 presumably represents the sex chromosomes. 



In specimen 2055 there are normally two, equal sized, spherical 

 nucleoli in the early growth stages. Just before the nucleus 

 begins to become lobulated the tw r o nucleoli come close together 

 and apparently unite, although it is possible that one may de- 

 generate after they become approximated. Following this the 

 nucleolus becomes bilobed as in specimen 2056, and subsequently 

 its history is the same as that of the latter. 



In both specimens the nucleolar structures are surrounded by a 

 hyaline cortical region similar to that of the autosomes, although 

 it may be noted that the cortex of the large, irregular portion is 

 usually thinner than that of the small, spherical part which prob- 

 ably represents the sex chromosomes. 



DISCUSSION. 



The constancy of the hyaline zone around the chromatic 

 threads in the nuclear lobes we interpret as indicating the presence 

 of a relatively soiid (gelatinous) cortical layer enveloping the 

 respective chromosomes. The presence of the layer is revealed, 

 of course, by the structure of the lobes. If the nuclei were 

 spherical it would not be detected. This raises the question as to 

 whether the condition is restricted to the present species, or is of 

 more general occurrence but usually invisible. 



We have noted above that evidence of the hyaline zone is to be 

 seen in spermatogonia as well as in spermatocytes of Lasiopogon. 



