A. GLENN RICHARDS 



159 



organ segregation is being completed) through into the adult stage. No 

 such omnipresent hormone is known. 



Finally, we found no visible pathology even at the mitochondrial level. 

 Tissues of all organs were examined in serial sections after staining with 

 Heidenhain's iron hematoxylin, the Feulgcn reaction, the periodic acid- 

 Schiff reaction for polysaccharides and aniline acid fuchsin-methyl green 

 for mitochondria. Whole mounts were also examined after staining with 

 Black Sudan B. Because of the interest to oxidative metabolism, these nega- 

 tive results are illustrated by photographs of mitochondria in oenocytes of 

 larvae from eggs incubated at 17° and 25° (fig. 11). Clearly, the mito- 

 chondria appear equally normal in both. 



But we do have one clue. The debility can be overcome in either embry- 

 onic or larval stages by warming the animals for a few hours daily (fig. 5, 

 line FF, and table 4) . In other words, if alternation from favorable (20°- 



5 >i 





Fig. 11. Photomicrographs of sections of freshly hatched Oncopeltus larvae in- 

 cubated at 17° antl 25°C showing similarity of the mitochondria in oenocytes. (Zirkle's 

 fixative, aniline acid fuchsin-methyl green stain, photographed with green filter.) 



30°C) to subthreshold temperature (13°-14°C) is made only once or a few 

 times, then some 60%-70% of developmental time (= >20% of actual 

 time) must be at the favorable temperature to produce hatching (more to 

 produce viable larvae) , but if the warm treatment is given in frequently 

 repeated small doses then less than 40% of developmental time (= <10% 

 of actual time) will produce both fair hatching and fair viability in those 

 that hatch. At favorable temperatures, that amount of time which when 

 given as short daily treatments will produce normal hatching and normal 

 viability (survival), will when given as a single warm treatment produce 

 a small hatching percentage with zero or nearly zero viability. Also note 

 that an average temperature of 15° gives much more viability when the 

 average temperature is produced by 4 hours at 25° plus 20 hours at 13° 

 than when it is produced by 2 hours at 25° plus 22 hours at 14°. It follows 

 that the average temperature is not of primary importance. When warm 

 treatments are given at frequent intervals, the length of time at the favor- 

 able temperature seems more important than the over-all temperature 

 average. 



