SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



663 



that in the early stages the eggs had a lower gaseous exchange 

 during the 2nd hour than during the ist, but that in the later 

 stages the reverse was the case, and the 2nd hour readings were 

 greater than the ist. This was interpreted to mean a decreasing 



60 



cs 50 



30 



20 



■bc 10 



Temperature 30°C 



Temperature 10° C 



10 20 30 40 50 60 70 80 

 Time in hours 

 Fig, 123 a (Buglia). 



100 110 120 130 



sensitivity with age to the effects of carbon dioxide in the ambient 

 sea water. Returning to Fig. 123 a, the curve at 21° should be taken 

 as normal, and from that it is clear that there are three periods in 

 the change of respiratory rate with time in the case of Aplysia, 

 {a) from o to 35 hours, {b) from 35 to 50 hours and [c) from 50 hours 

 onwards. The point marking the transition of period {a) to period {b) 

 is the complete surrounding of the endoderm by the ectoderm, while 



