260 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



eggs will develop into larvae without segmentation. In one 

 experiment the unfertilized eggs of a female were placed in 

 50 c.c. of sea-water + 1 . 5 c.c. N/10 NaOH and left for some time 

 in that solution. Four hours later all the eggs had formed a 

 definite membrane and extruded both polar bodies. After eight 

 hours a small number of the eggs were in the two-cell stage- 

 cleavage was quite normal but the rest remained undivided. 

 Twenty-four to forty-eight hours after the start of the experi- 

 ment the majority of the eggs had developed into swimming 

 larvae. But, externally, segmentation did not appear to have 

 extended beyond the two- or four-cell stage. The control eggs 

 that had been left in ordinarv sea-water had not matured, and 



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in the course of twenty-four hours they fell to pieces. This 

 oft-repeated experiment proves, therefore, that the unfertilized 

 eggs of Polynoe can be made to mature and develop into larvae 

 by exposing them for some time to hyperalkaline sea-water. 



But there is one important consideration that must be taken 

 into account, and that is a favorable supply of oxygen. The 

 eggs developed in large numbers only when contained in lightly 

 covered watch glasses, while the eggs left in the big dish in 

 which they were separated from the air by some 2 cm. of water 

 matured and developed in much smaller quantities. Perhaps, 

 too, the neutralization of surplus alkali by the carbonic acid 

 of the air is effected much more quickly in the watch glass 

 than in the larger dish. I convinced myself, however, that if 

 the eggs are transferred from the hyperalkaline to normal 

 sea-water, the formation of larvae occurs only if the eggs have 

 been at least from four to six hours in hyperalkaline sea-water; 

 and even then the results are much worse than when the eggs 

 remain all the time in the hyperalkaline solution. If, however, 

 the treatment with a hypertonic solution was combined with 

 that by alkali, less alkali could be used and more eggs segmented 

 and the segmentation advanced farther (especially in the case 

 of weak bases). 



