54 LIBBIE H. HYMAN. 



development were placed in tubes with the phenolsulphonthalein 

 solution in sea-water. The pH of the sea-water at Woods Hole 

 was found to be 8.2 by comparison with the set of standardized 

 tubes put out by Hynson, Westcott, and Dunning. The length 

 of time required for the forty eggs in a closed tube to turn the 

 indicator from pH 8.2 to pH 7.6 was recorded at different stages 

 of development. This furnishes a rough measure of the rela- 

 tive rate of carbon-dioxide output at successive stages. The 

 temperature was of course kept constant as nearly as practicable 

 throughout such experiments. 



The data on the oxygen consumption are given in Table I. 

 Four experiments were run, each consisting of over a thousand 

 eggs mixed from a number of females. Three of these experi- 

 ments were run simultaneously, the fourth one at a later time. 



The experiments recorded in Table I. show that the oxygen 

 consumption remains about the same through the early cleavage 

 although a slight rise probably occurs. By the time, however, 

 that the blastoderm has spread one third or half way over the 

 yolk a marked rise in the rate of oxygen consumption occurs. In 

 experiment 4 this rise was over 200 per cent., less in the other 

 three experiments. From this time on through the establishment 

 of the embryo the rate remains about the same and may even fall 

 again. Thus the formation of the embryo is not a period of 

 increase in the rate of oxygen consumption but rather the time of 

 high respiratory activity is that period when the germ ring is 

 approaching the equator of the egg. This probably corresponds 

 to the time of gastrulation. After the heart has begun to beat 

 the oxygen consumption rises again as also found by Scott and 

 Kellicott. Beyond this time the determinations yielded rather 

 irregular results. I cannot verify the statement of Scott and 

 Kellicott that there is a general upward trend during these later 

 stages ; I found a considerable variability in the amount of 

 oxygen consumed ; in general it was very little if any higher than 

 the rate at the time the heart had begun to beat vigorously. In 

 the table the average of these later determinations is given. It 

 should be emphasized that the determinations during later stages 

 are probably unreliable owing to the growth of bacteria on the 



