72 HARRIETT M. ALLYN. 



EXPLANATION OF PLATE II. 



FIG. 7. Uninucleate, unicellular, swimming larva. Treated as described for 

 Fig. 6. One or two very small nuclei and several ragged masses of chromatin are 

 seen outside the main nucleus. The yolk mass is chiefly in the half of the egg 

 nearer the animal pole. Two polar bodies have been thrown out. 



FIG. 8. Blastula. Egg treated with 3.5 c.c. 2 l / 2 M KC1 + 96.5 c.c. sea-water 

 until the formation of the second polar body, then with sea-water through which a 

 constant current of oxygen was passing. Fixed 4 hours after the beginning of the 

 experiment. 



FIG. 9. Four cells of a six-celled specimen which had been subjected to sea- 

 water heated to 32.5 C.-34-5 C. for 40 minutes. Fixed 3 hours and 15 minutes 

 after the beginning of the experiment. 



FIG. 10. Blastula. Egg treated as described for Fig. 9. Fixed 7 hours and 

 5 minutes after the beginning of the experiment. 



FIG. n. Larva. Egg subjected to sea-water heated to 33 C.-34-2 C. for 

 42 minutes. Fixed 21 hours and 16 minutes after the beginning of the experiment. 

 Other larvae of similar appearance were ciliated. 



