70 HARRIETT M. ALLYN. 



EXPLANATION OF PLATE I. 



All figures were drawn with camera lucida with Leitz apochromat 2 mm. oil 

 immersion objective, and Zeiss No. 6 compensating ocular, except Fig. i for which 

 compensating ocular No. 12 was used. 



FIG. i. Egg fixed after remaining 30 minutes in 7.5 c.c. of 2% M KC1 + 92.5 

 c.c. of sea-water. The second maturation spindle is seen lying deep within the 

 cytoplasm of the egg. Two chromosomal vesicles are shown at either end of the 

 spindle. (It is entirely normal for these vesicles to arise in the formation of the 

 nuclei after division.) 



FIG. 2. Egg fixed after 35 minutes in 3.5 c.c. 2^/2 M KC1 + 96.5 c.c. sea-water. 

 The second polar nucleus and female pronucleus are about to unite to form the 

 cleavage nucleus. The first polar body was seen in another section. 



FIG. 3. Egg remained in 7.5 c.c. 2 l /% M KC1 + 92.5 c.c. sea-water 60 minutes. 

 Fixed five hours after the beginning of the experiment. Rods and granules of 

 chromatin are seen migrating out from the nucleus into the cytoplasm. 



FIG. 4. Egg treated as described for Fig. 3. Rods of chromatin previously 

 cast out of the nucleus are seen lying in the cytoplasm. The nucleus is in the 

 achromatic state. 



FIG. 5. Egg remained in 7.5 c.c. 2*/ M KC1 + 92.5 c.c. sea-water 60 minutes. 

 Fixed 14 hours after the beginning of the experiment. The figure represents an 

 egg in the process of becoming multi-nucleate. Nuclei appear to be "condensing" 

 from a large mass of scattered granules. Two polar bodies are shown. 



FIG. 6. Multi-nucleate, unicellular, swimming larva. Egg treated with 3.5 c.c. 

 2^ M KC1 +96.5 c.c. sea-water 45 minutes. Fixed 14 hours and 15 minutes 

 after the beginning of the experiment. A circle of nuclei surround a mass of yolk 

 material and cytoplasmic granules. 



