I/O M. LOUISE NICHOLS. 



I 



Sometimes the karyosphere is formed immediately after syn- 

 apsis. Illustrations of this are furnished by the oogenesis of 

 the dragonfly, PUitln-mis (McGill, 1906), and the pollen develop- 

 ment of Sarracenia (Nichols, 1908). In this plant the karyo- 

 some is formed from the synaptic threads through an absorp- 

 tion of the chromatin substance by a nucleolus (Plate III., Fig. 

 i). The achromatic substance (linin) remains as a dense mass 

 after the chromatin has passed by drops into the closely con- 

 tiguous nucleolus. There is, therefore, a rather conspicuous 

 separation here of chromatin and linin. 1 



In Plathemis the synaptic threads gather closely around the 

 nucleolus and form what Miss McGill calls a double nucleolus 

 (oxyphil + basophil). There is plainly an interchange of material 

 between the two parts of the nucleolus and, as the network 

 again expands, masses of basophil substance are elaborated 

 within the nucleolus and pass out on to the network. 



In Euchroma the transfer of chromatic material to the kary- 

 osome is less direct, inasmuch as the synaptic threads are first 

 extended into the network of the resting spermatocyte (Fig. 10; 

 Plate III, Fig. 4, a). The latter possesses no large nucleolus such 

 as is present in the plant nucleus. Nevertheless a center of activ- 

 ity arises, towards which the chromatin passes and simulta- 

 neously also the linin, at first in the form of streamers radiating 

 from the karyosphere (Figs. 11-12). Later, as the chromosomes 

 become distinct within the karyosphere, the linin is incorporated 

 with them (Figs. 16-18). 



Blackman (1903) interprets the karyosphere of the spermato- 

 cytic prophase of myriapods as a mass of fine, granular filaments 

 closely gathered about the accessory chromosome. As the 

 nucleus approaches mitosis, the threads emerge from the karo- 

 sphere, shorten and thicken to become the mitotic chromosomes 

 (Plate III, Fig. 3, a and b). There is here no separation of chro- 

 matic from achromatic substance, only a strong attraction for both 

 to a definite region of the nucleus. As compared with Euchroma 

 this tendency manifests itself much earlier, for the karyosphere 

 has already begun to resolve itself into definite chrojnosomes in 



'A closely similar behavior of chromatin has been described for Spirogyra by 

 Berghs (1906). 



