A. GLENN RICHARDS 



155 



perature only the heavier eggs have enough available stored reserves to go 

 throuoii hatcliing. 



The above correlation is so reminiscent of variation found by Lin cf al. 

 (8) in hatching percentage curves (fig. 3, curves A and A') that the present 

 author is inclined to go a step further and to suggest that the wide variation 

 in hatching curves at minimal conditions is primarily due to variation in 

 egg size in different samples of eggs. 



If the hatching threshold is simply an expression of the point at which 

 exhaustion of available reserves occurs one would not necessarily expect to 

 find any organ or tissue pathology associated with the threshold — and in- 

 spection of serial sections stained in various ways revealed no pathology. 



Table 3. Measured and estimated values for variation in results of 

 incubation of oncopeltus at threshold temperature of 15° c* 



Weights in micrograms. Estimated values given in parentheses, see table 1. 



Implicit in the above presentation is the idea that the stored reserves are 

 completely exhausted at subthreshold temperatures. Direct histological 

 examination shows this is not true. Serial sections show that larvae un- 

 successful at hatching at 15° (some of the semi-hatched ones of table 3) 

 still had considerable quantities of yolk enclosed in the midgut (fig. 8). 

 And extirpated midguts showed a little Sudan staining. Calculations show 

 that the fat loss at 14° should equal or exceed the amount available but 

 there would presumably still be some albuminous yolk present. Since this 

 histological evidence shows that the stored reserves are not completely ex- 

 hausted, and since eggs can hatch at average temperatures of 14° although 

 not at a constant temperature of 14° (see table 4) , further work will be 

 necessary to determine whether some particular component of the food 

 reserves is exhausted or whether the phenomenon is complicated by some 

 additional factors such as that to be discussed in the next section. 



