INDIVIDUALITY OF THE GERM-NUCLEI. 263 



vesicle, and that in the prophase the chromatin concentrates 

 about this remnant or core and there forms a spirally coiled 

 thread, which develops into a prophase chromosome." Richards 

 (1917) has shown that in the cleavage and gastrula stages of 

 Fundulus and Coregonus the chromosomes in the telophase of 

 mitosis enlarge to form vesicles which remain distinct though 

 compactly massed together during the resting stage. The new 

 chromosome arises within a vesicle, through the aggregation 

 of its granules; thus there is genetic continuity of individual 

 chromosomes. According to Richards, the polarity of the cell 

 is manifested in the arrangement of the elongated vesicles. 

 When the centrosome divides, the cell acquires a new axis at 

 right angles to the old, in a line connecting the two asters; the 

 chromosomes, when formed, orient themselves with respect to 

 the new axis. Pinney (1918) figures chromosomal vesicles in the 

 telophase of dividing blastomeres of Ctenolabrus X Fundulus 

 hybrids. Some observations on chromosomal vesicles in Crypto- 

 branchus allegheniensis are included in the present paper. I have 

 examined a few sections of Coregonus blastoderms belonging to 

 the collection of the Michigan State Normal College and the 

 material appears to be exceptionally favorable for the study of 

 chromosomal vesicles. 



Thus it has been proved that in the fertilized egg one half of 

 the chromosomes are derived from the father and one half 

 from the mother, and that at every division of the egg the chromo- 

 somes also divide in such a manner that their progeny are dis- 

 tributed in equal number to all the cells of the egg. Further, 

 there is genetic continuity between each individual chromosome 

 that enters the resting stage and a corresponding chromosome 

 that emerges in preparation for the next division. The con- 

 clusion is thus reached that the fertilized egg, and all the cells 

 derived from it, contain a double set of chromosomes, paternal 

 and maternal. This conclusion implies that at every step the 

 respective chromosome groups preserve their independence, how- 

 ever much they are mingled with one another. 



This conclusion is further strengthened by observations of 

 individual differences, both morphological and physiological, 



