S Papers from the Marine Biological Laboratory at Tortugas. 



complete dispersal of the definite and sharply contoured resulting bodies of 

 the full-grown nucleus. In Asterias forbesii germinal vesicles were occa- 

 sionally found in which were scattered as many as fifty or more small chro- 

 matic masses. These were interpreted as abnormalities or the result of 

 degeneration. But in this case the bodies were always larger or smaller 

 globes and were found only in the younger eggs. Nor could the nucleolus 

 ever be seen as a whole to break up into such. The striking thing about 

 Ednnaster is the change of these elements from a globular form to definitely 

 four-lobed bodies. 



The case seems to be very clear for Echinaster crassispina that here the 

 chromosomes arise exclusively from the nucleolus, the latter not even leaving 

 a plastin remnant behind. The function of the germinal spot here seems to 

 be wholly that of a storehouse of chromatin for the chromosomes, the latter 

 being apparently, at least during the early history of the growth-period, 

 compacted into one solid homogeneous mass or chromatin nucleolus, and 

 their separate individuality merged into one common chromatic whole. It 





& ^-^ f TF^fa* 8 



f^Irtk 4 -/ 



6 7 



FIG. 6. A number of chromatic bodies from portion of a single nucleus; the majority 



have the form of tetrads and several are arranged in shape of chromatic threads. 



X 1500. 

 FIG. 7. Portion of cytoplasm from an ovum at culmination of growth-period. X 1500. 



would be most interesting to observe here the final telophase of the oogonial 

 division, and to study the process of synapsis and the construction of the 

 nucleus and nucleolus of the resting stage of the oocyte. The eggs are of 

 such goodly size that this part of the investigation seems very promising. 



All that the present material yields of definite fact is that the chromo- 

 somes arise as the products of a process of fragmentation of the nucleolus. 

 Nor is the nucleolus here a double structure, though in the very early stages 

 there is indication of a plastin ground-substance. But concerning the com- 

 plete function of the chromatin nucleolus, its relation to a true nucleolus or 

 plasmosome, as also its relation to an accessory chromosome, and concerning 



