Respiration and Metaholism 



231 



In the earlier stages of embryonic development there appear abrupt changes 

 in the respiratory exchange, correlated with profound developmental mile- 

 stones as cleavage, gastrulation, diapause, metamorphosis, and fertilization 

 itself. Years ago Warburg-*''" demonstrated a seven-fold increase in oxygen 

 consumption in Arhacia eggs at the time of fertilization, a phenomenon ade- 

 quately substantiated on a number of other forms. In Fundulus, besides the 

 increase at fertilization, a second marked increase occurs at about the time 



200 



10 - 



20 

 AGE 



30 



M 



Fig. 49. Decrease in metabolic rate with age of several birds and mammals. Age in 

 months, except for man in years. After Benedict and Talbot." 



when the vascular system begins to flourish. That all embryonic forms do 

 not follow the same respiratory pattern, however, is clear from the work of 

 Tang'^'^" on the starfish and that of Brachet"*^ on Amphibia, which show no 

 increase in oxygen consumption at fertilization. In fact, the clam, Cwningia, 

 and the annelid, Chaetoftenis, undergo a decrease in oxygen uptake at the 

 time of fertilization.'*"-' •^"■' An increasing metabolic rate of rat eggs during 

 early cleavage is correlated with an increase in volume, in turn attributed to 

 water uptake and probable yolk-protoplasmic conversion.'*" For an extensive 

 review of the literature concerning embryonic metabolism, the reader is 

 referred to the thorough treatment by Needham--^'-' and Boell.-^*^ 



