BARBARA LEE LUND. 



minutes, and so it is uncertain as to whether there was a second 

 and a third susceptible period after the first and second cleavages. 

 He also investigated the effect of heat and cold on developing 

 sea urchin eggs (Lyon, '04) and found that immediately after the 

 entrance of the sperm the egg is more susceptible to heat than 

 a few minutes later. The resistance decreases, reaching a low 

 point just before division, then increases, reaching a maximum 

 right after division, decreasing again to a low limit just before 

 the second division. Similar experiments were performed with 

 cold but they were not carried beyond the first cleavage, so here 

 no rhythm was demonstrated, but he considers the existence of 

 such a rhythm probable. Lyon ('04) also studied the carbon 

 dioxide production of the developing sea urchin egg. His experi- 

 ments here were not strictly quantitative in character, but he 

 found a slight increase in COo production in the first ten to 

 fifteen minute interval following fertilization. Decreased CC>2 

 production followed. The interval during which the eggs were 

 actively dividing into the first two blastomeres was one of 

 active CO. production. This was followed by a period of lessened 

 production with a second rise at the time of the second cleavage. 

 Spaulding ('04) also found decided rhythms in the resistance of 

 the developing sea urchin egg to both ether and hydrochloric 

 acid. Mathews ('06) made a study of living eggs of Arbacia 

 and Asterias and examined sections of eggs preserved at definite 

 intervals after fertilization. Comparing Lyon's work on Arbacia 

 and the condition of the egg at the various intervals, as shown 

 by the sections, he concludes that the period of greatest suscepti- 

 bility is immediately before and during segmentation, and that 

 just after segmentation there is a period of great resistance. 

 He also endeavored to repeat Lyon's work on Arbacia, using 

 Asterias eggs. The results were unsatisfactory so far as sharp 

 and decisive periods of susceptibility were concerned, but they 

 showed clearly that the eggs in certain stages were more suscep- 

 tible to KCN than in others. 



Moore ('15), in his work on artificial parthenogenesis, found 

 that the greatest number of eggs, which had been previously 

 treated with butyric acid, developed when treated with the 

 hypertonic sea water at 40, 60, 90-100 and 115-125 minutes 



