202 



PRINCIPLES OF EMBRYOLOGY 



ventral regions. Boell and Needham (1939) used, the Cartesian diver to 

 obtain more accurate measurements of the respiratory quotient (oxygen 

 uptake divided by COg output). They found that in the blastula roof the 

 respiratory quotient is about 075. By the mid-gastrula, this has risen to i 

 in the blastopore region, but is still only about 08 on the ventral side, 

 where it rises much more slowly and does not surpass about 9 by the 

 end of gastrulation. 



A respiratory quotient of unity is often taken to indicate that the 

 respiratory metabohsm is involving the breakdown of carbohydrate 



L- LIQUID! 

 -' ^^, ,^ LIPOID 

 --SOLID 





PERCENTAGE YOLK 



- -SOLUTION- 

 SALTS, 

 PROTEIN ETC. 



PRECIPITATED 

 .- PROTEIN 



__ PIGMENT I 



HYALINE LAYER 



PIGMENT!! 



YOLK 



'02 



20 40 60 80 



'active' material 



Figure 10.14 



On die left, a diagram of the stratification of gastrula tissues following high 



speed centrifiigation. On the right, the respiratory rates of the various 



regions of the gastrula plotted against their content of 'active' material (i.e. 



everything except yolk). (From Boell 1948.) 



rather than of fat or protein. There is independent evidence that this is in 

 fact the case in the amphibian organiser region. Woerdemaim (1933) 

 claimed, on the evidence of histochemical investigations, that glycogen 

 disappeared from the presumptive mesoderm cells as they invaginate 

 through the blastopore. Although Pasteels disputed the validity of his 

 methods, Heatley and Lindahl (1937) demonstrated by microchemical 

 analysis that there is a rapid fall in the glycogen content of the invaginating 

 cells, although it does not disappear entirely. 



The Cartesian diver studies also showed that the rate of anaerobic 

 glycolysis is about three times as high in the blastopore region as it is on 



