383 



the unsectioned nuclei; sections, however, show that the meshes are 

 much smaller than in the 17 — 26 mm stages, resembling in general 

 the condition observed in the 7 — 10 mm stages. 



Plasm osomes are always present. They are not disposed regularly 

 but may be found in almost any part of the nucleus. The condition 

 most frequently observed is that shown in Fig. 3 where a single 

 plasmosome is found in either end of the nucleus. 



The karyosomes (k) are far less numerous than in any of the 

 preceding stages. They are likewise smaller and as has already been 

 stated possess less affinity for nuclear stains. They never aggregate 

 to form a peripheral layer but usually he well within the nuclear 

 membrane, irregularly scattered and quite widely separated. 



It may be here remarked that while the changes in the nuclear 

 membrane and linin network are obvious, those occurring in the 

 plasmosomes and karyosomes are more striking. 



The number of plasmosomes in the nuclei of the 6—7 mm embryos 

 vary from two to five, and are readily stained. As differentiation ot 

 the fibrillae proceeds (8 — 9 mm) they decrease in number and show 

 a greater affinity for the various basic stains. With the increased 

 cytoplasmic activity (17 — 26 mm) these structures entirely disappear. 

 In the old nuclei (23 cm) they have reappeared, although fewer and 

 with less affinity for basic stains. 



The changes in quantity, quality [and distribution of chromatin 

 during the various phases of cytoplasmic differentiation are most 

 remarkable. In the early stages (6—7 mm) the karyosomes are com- 

 paratively small and quite evenly scattered throughout the nucleus; 

 soon however (10 mm) the chromatin shows a tendency to aggregate 

 in larger karyosomes which are irregulary disposed. These larger 

 masses of chromatin undergo further aggregation until they (17 — 26 mm) 

 become grouped into a peripheral layer; in addition to which there 

 are usually a few scattered axial karyosomes. It is important to 

 remark in this connection that the peripheral layer of chromatin is 

 much thicker on the side which comes in closest relation to the 

 fibrillated portion of the cytoplasm. 



This peculiar condensation of chromatin, being more accentuated 

 on the side of the nucleus which is applied to the fibrillated surface, 

 suggests that a condition is thus brought about which is most favor- 

 able for the correlation of nuclear and cytoplasmic activity. While I 

 know of no observations which are of precisely the same nature there 

 are many which show that there is a marked increase in the contact 

 surface of the nucleus during phases of great cytoplasmic activity. 



