1913] Variation in the Genus Lucilia. 247 



The width of front affords a secondary sexual character. 

 In the males the front was from one-tenth to one-twelfth 

 head width. Hough gives the width as "very narrow" and 

 "one-eighth to one-tenth head width. " A better way is perhaps 

 to say that the width of front in cf L. sylvarum comes interme- 

 diate between that of L. caesar, which is linear, and that of L. 

 sericata which is from one-seventh to one-eighth head width. 

 Once having examined specimens as to this character in males 

 of all three species it becomes a comparatively easy task to 

 subsequently reduce any male Lucilia, on this character alone 

 to its species. 



The front of the females was found to be somewhat nar- 

 rower than in L. sericata and about the same as in L. caesar. 

 In actual width it was found to be about 3-10 (measurements 

 were made in a number of specimens) of the head width; this 

 is slightly less than 1-3 head width. This character serves 

 very nicely for separating females of this species and of L. 

 caesar from females of L. sericata which have a front measuring 

 4-10 head width, or slightly greater than 1-3 head width. 



The color of the palpi appears to be far more constant 

 in this species than in L. sericata. This color was dark brown 

 or almost black in all but two cases and in these it was black. 

 The color of the dorsum of the first abdominal segment was 

 not in this case found to afford a secondary sexual character as 

 in L. sericata^ In the females the first abdominal segment 

 was either blackish or black, and in the males it was black. 



A comparative study of the bristles of the second abdominal 

 segment produced some curious results. In the case of L. 

 sylvarum one bred male had a strong pair of median marginal 

 bristles and no differentiated marginal row. 68% of the females 

 in the same lot had a strong central pair of bristles and a weak 

 marginal row ; several flies had the central pair no stronger than 

 the remaining bristles of the marginal row. Again in another 

 lot of bred material of 7 females two exhibited this latter con- 

 dition of having the central pair no stronger than the others. 



This variation is important because the presence of a pair 

 of strong median marginal macrochaetae has always been 

 attributed by writers to L. sylvarum and here it is shown that 

 the character may vary to quite a considerable extent. 



In most cases the central pair were of about the same 

 strength as the remaining bristles. As a rule, however, these 



