1913] 



Vafiation in the Genus Lucilia. 



251 



accompanying diagram showing the positions of these thoracic 

 bristles in the case of seven flies all bred from a single parent 

 indicate this variation better than can any description. . 



The point is of interest on account of the fact that Mr. 

 Townsend (loc. cit. p. 121) in describing a new species of 

 Lucilia (L. girauUi) makes use of the relative positions of the 

 postacrostichal and dorsocentral bristles. 



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Diagram 



Showing variation in relative position of dorsocentral and postacrostichal bristles 



in the case of 7 specimens of L. sericata, all bred from the same parent fly. 

 Legend: 



Each dot within a circle represents the insertion of a bristle. 



Each bracketed group (of the total 7) represents the dorsocentral and posta- 

 crostichal bristles of one fly. 



The two outside rows of bristles are dorsocentrals. 



The two inside rows of bristles are postacrostichals. 



The chief value of this study in variation lies in the fact 

 that each species dealt with was found to be subject to con- 

 siderable variation in the matter of chaetotaxy, color, size, etc. 

 Also in that all the new characters used by Mr. Townsend (loc. 



