SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



66 1 



reached its minimum at the time when the embryos were curved 

 like a U, and it rose again during the main period of increase in 

 length and the assumption of mobihty by the embryos. If, then, 

 the Ascaris egg is burning its reserves completely to carbon dioxide 

 and water, it could be stated roughly that a period of protein 

 or mixed fat-protein combustion was succeeded by a period of 

 carbohydrate or mixed protein-carbohydrate combustion. 



Later work by Brown shows that a difference of temperature has no 

 influence on the amount of oxygen taken up by nematode eggs during 

 their development, but only affects the rate at which this process 

 occurs^. Zavadovski has found that also in the case of the nematode 

 tg^ {Ascaris) cleavage is stopped by lack of oxygen or by certain 

 1.00 



c 0.90 



Hours 



Fig. 122. 



concentrations of potassium cyanide. He has brought forward 

 evidence showing that this egg has two kinds of oxidation-processes, 

 one group affected by potassium cyanide and the other not affected, 

 and that cell-cleavage is associated with the former group. Reznicenko, 

 like Zavadovski, has studied the effect of potassium cyanide (in large 

 amounts) on the respiration of nematode eggs, but with paradoxical 

 results. 



Lite & Whitney have made some observations on the respiration 

 of rotifer eggs. These do not normally hatch for many weeks after 

 they have been laid, but if they are laid without a shell or with 

 only a very thin one they develop fast, and hatch in a comparatively 



1 This was confirmed by McCoy for the eggs of the hookworm, Ankylostoma caninum. 

 These are exactly the same size as Ascaris eggs and take up the same amount of oxygen 

 from fertiHsation to hatching, aUhough their speed of development under the same con- 

 ditions is 21 times as fast. High oxygen tensions inhibit development of hookworm eggs. 



