STUDIES IN ARTIFICIAL PARTHENOGENESIS. 189 



has been stated to produce parthenogenesis in the sea-urchin 

 egg (McClendon '10). Lowered temperatures should result 

 in an increase, rather than a decrease of surface tension, nor 

 can they be thought of as causing exosmosis. 



In the only experiment tried, I found that instead of producing artificial par- 

 thenogenesis, lowered temperatures tended to retard the natural parthenogenesis 

 which is usually manifested by the Arbacia egg. On June 25, the temperature of 

 the aquarium in which the sea-urchins were kept, was 19.5, the temperature of the 

 sea-water as it emerged from the tap was 19; the room temperature (at 4.45 P.M.) 

 was 24.5. At 10.40 A.M., a beaker containing eggs in a small amount of sea- 

 water was placed in a large beaker, and the space intervening between the two 

 beakers was filled with cracked ice. The beakers were then placed in the ice-box. 

 At ii. oo A.M., the temperature of the sea-water surrounding the eggs was 3.5, 

 at 11.35 A.M. it was 1.5, at 2.15 P.M. it was 0.5, and at 4.15 P.M. it was 1.5. 

 Eggs were transferred from cold to normal sea-water after 3! hours (2.15 P.M.), 

 5 hours (3.40 P.M.), and 6\ hours (5.05 P.M.). We can refer to these three lots 

 of eggs as lot A, lot B, lot C, respectively. 



Lot A when counted at 4.30 P.M. showed one doubtful case of segmentation, 

 out of 100 eggs observed. 



Lot B at 5.30 P.M., out of 1,000 eggs counted, showed 3 eggs apparently cleaving 

 irregularly, and i doubtful case. At best 4/1000. 



Lot C at 8.55 P.M. showed 9/1000 cleavages. 



The control of untreated eggs (from the same female) at 4.40 P.M. showed, 

 of 1,100 eggs counted, 4 eggs cleaving irregularly (i a 7-celled stage) and 5 with 

 attempted or incomplete cleavages. At 9.05 P.M. however, the control showed 

 a much higher count. Of 526 eggs counted, 36 showed irregular divisions. Thus 

 of the eggs counted at about 9.00 o'clock, those which had been exposed to cold for 

 6| hours showed less than i per cent, of segmenting eggs, whereas the control 

 showed over 6 per cent. Thus the cold evidently retarded the process of natural 

 parthenogenesis. 



Of the two general methods of obtaining parthenogenesis, 

 the exosmotic method yields the better results. Usually the 

 endosmotic method produces only a small per cent, of segmenting 

 eggs. But this is probably due to the specific poisoning action 

 of the substances used in lowering surface tension, for when 

 the sea-water is simply diluted, or when a harmless substance 

 like egg albumen is used, much higher per cents, of dividing 

 eggs are obtained. For example, when eggs were subjected to 

 the action of a i per cent, solution of egg albumen (Kahlbaum) 

 in sea-water, more than half of them divided, as shown in the 

 accompanying table. In such a solution, the eggs were observed 

 to undergo membrane swelling (see p. 173) and this was followed 

 bv endosmosis as shown bv the increased diameter. 



