72 William B. Herms 



one adults emerged, whence the numher used in this series. 

 The mean weight shows a remarkable selection, since the average 

 weight of the adults is greater in this series than in the preceding 

 series, and yet the mean weight of larvae is less, that is to say, the 

 lighter weight larvae did not produce adults. 



Series 6 — In this series with a feeding period of thirty-six hours 

 we reach the lower limit at which adults could be secured. The 

 smallest fully (developed flies of Lucilia ccesar weighed about four 

 milligrams, though several emerged that weighed but half that 

 much, but died before the wings were spread. Several also died 

 in struggling to free themselves from the pupa cases. As men- 

 tioned before the pupa cases of these light forms are very flimsy and 

 are also gummy, thus making it more difficult for the young 

 imagines to emerge from such a case. 



Note I — The weights given above for imagines are of flies that had no opportunity of feeding, the 

 weight being taken within an hour or two after emerging from the cases. For comparison the individual 

 weight was taken of sixty-four specimens of Lucilia caesar, regardless of sex, feeding out of doors on fish. 

 The range of weight was quite wide, varying from 14 mg. to 72 mg., however, only three were above 60 

 mg. The average weight of this group is 38.17 mg. As compared with the adults of the optimum 

 series (22.28) the above average seems very great. This can be accounted for by the presence of numer- 

 ous ova in various degrees of development within the females and also by the presence of liquid food 

 that is contained within the alimentary canal of each individual. 



Note 2 — It was the plan of the writer to secure the normal frequencies of Sarcophaga sarraceniae, but 

 the great variation in weight required more individuals than there was time for weighing. After weigh- 

 ing several hundred larvae at migration, the result showed a range of weight from 75 mg. to 227 mg., 

 and in no class were there more than eight variates. No less than five thousand larvae would be necessary 

 to establish the normal frequency of this species. This wide variation in larvae at migration means also 

 a wide variation in pupae and imagines, which was also partly worked out. 



Tables showing the distribution of frequencies in Lucilia caesar: 



TABLE V 



Larva at migration 



Classes.. I25I26I27I28I29I30I31I32I33I34I35I36I37I38I39I40I41I42I43I44I45I46I47I48I49I50I51I52I53I54I5SI56I57 

 Variates | i| i| i| o| 3I 6| 4I 7] 7I13I18I25I30I24I23I22I16I15I15I ii| 5] z\ 2] 2| i| o| o| i| o| o| o| o| 1 



TABLE VI 

 Pupa weighed about the middle of the pupal period 



Classes. . 

 Va'riates 



[8I19I20I21I22I23I24I25I26I27I28I29I30I31I32I33I34I35I36I37I38I39I40I41I42I43I44I45I46 

 i| i| 2I z\ 6| q|i3|i6|i8|iq|3i|2o|2o|i9|2o|i7|i6| 9|i6|io| 6| 7I 5I o| 4I i| o| o| i 



TABLE VII 



Imagines weighed two or three hours after the wings were spread; no food taken 



Classes. . 

 Variates 



13I14I15I16I17I18I19I20I21I22I23I24I25I26I27I28I29I30I31I32I33I34I35I36 

 2I o| 3I 4I11I10I16I22I23I23I21 |2i|i6|ii| 8| 7I 3I i| i| 2I i| i| o| I 



