INITIATION OF DEVELOPMENT IN CH/ETOPTERl 5. 35 



either extruded or retained within the egg, where it unites with 

 the female pronucleus (see Figs. I and 2). After the eggs are 

 transferred to normal sea-water a period of imperfect cleavage 

 follows, which involves only the chromosomes. In the period 

 corresponding to first cleavage, imperfect and rudimentary 

 mitotic figures form and the chromosomes split longitudinally, 

 but do not separate into daughter nuclei. This process is re- 

 peated in subsequent divisions and the chromosomes remain in 

 an increasingly large, single mass, of tangled rods. This whole 

 period is characterized by a growth of the chromatin at the 

 expense of the cytoplasm Resting nuclei arise between suc- 

 cessive chromosome divisions, as normally, in Set B, but not until 

 several divisions have taken place in Set A, when a general 

 achromatic period enters. Shortly after this general resting 

 period in Set A, and perhaps a little earlier in Set B, a change in 

 general behavior follows. The nucleus begins to distribute 

 material to the cytoplasm, sometimes in the form of rods, more 

 often in the form of granules, a certain part of which become 

 indistinguishable in the cytoplasm as chromatin (see Figs. 3 and 

 4). Part of the chromatin in the cytoplasm seems to be "dis- 

 solved"; part forms small granules which are indistinguishable 

 from the small basophile granules of the cytoplasm ; part remains 

 as scattered chromidia. The chromatin in the nuclei of some 

 eggs also assumes new forms, short, stout rods, granular nuclei, 

 karyosomes, and irregular bodies of chromatin. Finally, a large 

 part of the chromatin distributed through the cytoplasm collects 

 in masses in various parts of the egg and forms membranes, thus 

 giving rise to accessory nuclei (Fig. 5). The latter part of 

 development may thus be called a period of chromatin distribu- 

 tion. It is during the latter period that the characteristic 

 cytoplasmic overflow described by Lillie ('06) takes place, 

 followed by the formation of cilia (Figs. 6 and 7). The process of 

 chromatin distribution seems to be definitely related to that of 

 cytoplasmic differentiation-. 



2. Sodium Chloride. The effects of sodium chloride were 

 similar to those of potassium chloride but not so good, therefore, 

 the solution was not used to any extent. Eggs in 8 c.c. of 2^/0 

 M NaCl + 50 c.c. of sea-water for 45 minutes, or for one hour 



