NUCLEOLI IN PEDICELLINA AMERICANA. 



353 



bryos examined, more than two nucleoli and these go through 

 all the typical transformations already described. The same con- 

 ditions are obtained in all the resting cells of the later embryos 

 up to and including the free-swimming larva ( Fig. 10 ). After 



FIG. 8. 



FIG. 9. 



the fixation of the latter, and the ensuing metamorphosis, the 

 young polypide, before stolon formation, shows the same inter- 

 esting conditions. We have thus traced the constitution of the 

 nuclei from the early polyp through the maturer ones, into the 

 formation of the germ-cells and finally, in the new generation, 

 have passed through the cleavage 

 stages up to the formation of the larva 

 and have completed the cycle with the 

 fixed polyp once more. 



From this evidence, coupled with 

 that of Riickert, '95, Hacker, '95- 

 '02, Zoja, '95, Herla, '93, Conklin, 

 'oi-'O2, and most recently of Moenk- 

 haus, '04, one might at first thought 

 conclude that in Pedicellina as in the 

 Copepods, etc., the nucleoli actually 

 express the internal relations of the 

 parental chromatins of the nucleus 

 and in their duality represent the 

 persistent segregation and autonomy of the paternal and 

 maternal chromosomes. This conclusion, however attractive, 

 has on close examination of the evidence not only in Pedicel- 

 Una, but in the other forms as well, a source of serious diffi- 

 culty. From the recent work of Moenkhaus, '04, above men- 

 tioned, it is clear that while the two nucleoli may be very 



FIG. 10. 



