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THE AMERICAN NATURALIST [Vol. XLVIII 



sealed. At the same time other bottles were very loosely 

 covered with a light cotton plug. The bottles remained 

 covered till flies had been hatching for four or five days 

 and then the plugs were removed and the flies counted. 

 The paraffine plugs were not replaced; after carefully 

 renewing the air in the bottles, they were covered with 

 cheese cloth and their brood counted again in four days. 

 The results of this test are given in Table XXXII. The 

 results are striking enough at first sight, but I do not 

 know just what their significance is. They show exactly 

 the same phenomenon that is described earlier and illus- 

 trated in Table III. They are more striking than any 

 case I have yet found of the sort, and yet the first infer- 

 ence drawn, viz., that the markedly higher percentage of 

 Beaded flies in the first count is due to these flies having 

 undergone their late development in a " close" atmos- 

 phere, must be qualified by the statement that " close" 

 does not refer to the carbon-dioxide content. 



At first suspecting this to be the case, I made an appa- 

 ratus by means of which fresh air could be drawn through 

 a bottle during the entire development of the brood. By 

 this means the carbon-dioxide content could not become 

 very high. In order to prevent drying out, a large amount 

 of food was put into the bottle and the air which was to 

 enter the bottle was first passed through water. The 

 hatching period was prolonged in the cool sink. The re- 

 sults were decisive. One hundred and sixty-nine flies 

 were hatched in the first four days, of which 32 per cent, 

 were Beaded. One hundred and eighty-four flies were 

 hatched in the next four days, of which 10 per cent, were 

 Beaded. 



The same flies that were the parents of this brood were 

 in the meanwhile transferred to another bottle, which was 

 covered with paraffine. The first four days of hatching 

 gave 108 flies, of which 15 per cent, were Beaded. 



This case shows conclusively that the carbon-dioxide 

 content of the bottles is not the feature of the closed 

 bottles that determines whether or not a fly shall have 

 Beaded wings. It leaves the question still unsettled as 



