OF WASHINGTON, VOLUME XIII, 1911, 177 



Dr. Lutz then discusses in detail the structures of the 

 imago. He dwells at some length on the finer structure of 

 the integumentary surface, which on the head and the thorax 

 produces the spots of pearly luster, or the white incrustation 

 and the like, which are constant for the species and therefore 

 valuable for classification. One must, however, guard against 

 poorly preserved specimens. 



The palpi of the imago are generally considered four-jointed; 

 only Schrottky indicates five segments. Lutz very rightly 

 takes exception to this view. Lutz finds that in the species ex- 

 amined by him the basal segment is ' often partly or wholly 

 divided by flexible integument and for this reason has been 

 considered as two segments. Similar conditions occur in the 

 Culicidse, but they have not the deep significance which, a 

 priori, one would be inclined to give them. 



As in many other blood-sucking insects, the abdomen is 

 capable of extraordinary distension. This is made possible in 

 two ways. When unexpanded the abdomen is strongly folded, 

 either longitudinally or transversely, The longitudinal folds 

 are not present in all the species, although in many of them. 

 Therefore they may serve occasionally as a distinguishing 

 character. The folds are generally most plainly visible on the 

 under side of the basal segments. These folds already are 

 present when the imago is still within the pupa; therefore 

 they are not due, as one might suppose, to shrinkage follow- 

 ing extreme expansion. Transverse folds, like the bellows of 

 a camera, are brought about by very deep constrictions be- 

 tween the segments. The margins of the segments, which 

 are thus hidden in the contracted condition of the abdomen, 

 are often lighter colored and become plainly visible when the 

 abdomen is distended. Generally one or the other type of 

 folds predominates, but also they can be developed equally. 



Lutz states that the coloration of the body is fairly con- 

 stant. Owing to the fact that the images issue from the 

 pupa fully developed and ready to fly no immature specimens 

 are met with. Still, there is some variation in certain species. 

 Occasionally very dark specimens occur, which he thinks may 

 be due to previous blood-meals. In some living specimens of 

 Simulium scutistriatum he observed that after they had been 

 fed with blood the entire body, inclusive of the legs, became 

 considerably darker. 



For the determination of species the character of the hair 

 and scale vestiture has proved of the greatest value. However, 

 Lutz protests against the possible employment of these char- 

 acters to create genera or sub^enera. Hairs and scales show 



