254 GASTRULA-ARRESTED EMBRYOS 



neither for nor against this postulate. Analogous considerations 

 can be advanced for the other indeterminate cases. The best we 

 can say is that all these cases remain consistent with the data now 

 on hand. 



The remaining cases — (6), (13), and (15) — are supported in- 

 discriminately by information that we now have. That is to say, if 

 any of these is the state of affairs in hybrid embryos, then we 

 should expect the hybrids to exhibit subnormal rates of oxygen 

 uptake, glycogen utilization, and anaerobic lactate production, 

 and to produce little or no aerobic lactic acid, and this, in fact, is 

 just what they do. 



In summary, there are eleven mutually exclusive general pos- 

 sibilities for blocks in hybrid carbohydrate metabolism which 

 must be investigated further before we can decide which of them, 

 if any, actually occur. And this leaves entirely out of considera- 

 tion all other sorts of biochemical deficiencies not directly in- 

 volved with the schema just discussed, not to mention the details 

 of the system that schema represents. 



Phosphorus Metabolism 



Hybrid embryos, clearly, are somewhat deficient energy pro- 

 ducers. For this reason, they ought perhaps to find it difficult to 

 maintain their stores of esterified phosphorus, especially when 

 put under stress by being made to develop under conditions 

 where energy production is even further curtailed. In 1947, Barth 

 and Jaeger made some measurements designed to answer the 

 question whether hybrids are as well able as R. pipiens embryos 

 to meet the stresses imposed by anaerobiosis. Their results (Table 

 I ) are summarized below : 



1. Aerobic hybrid embryos have been shown not to exhibit a 

 probably significant difference from R. pipiens controls in respect 

 of inorganic phosphorus (I) or ATP-ADP phosphorus (E?). 



2. Under anaerobiosis: (a) R. pipiens gastrulae exhibit a prob- 

 ably significant elevation of I, but no significant change in E- is 

 indicated; while (h) hybrid gastrulae exhibit a significant in- 

 crease in I and also a probably significant decrease in Et. The 



