Si 



KNOWLEDGE. 



[Februaky 1, 1900. 



This 

 flowers, 

 having 

 plant." 



fly may be seen on a sunny day hovering over 



or busy with the pollen, and is described as 



a " characteristic quiet manner of moving on a 



Fig. 4. — Hind leg of S. pipiens ; the smaller circle shows the 

 processes on the edge of the femur and tibia more magnified. 

 X 22 diameters. 



It will be seen on examination of the mouth organs 

 (fig. 3) that there are no pseudo trachse on the labella 

 of the proboscis, and no teeth ; also on looking at the 

 smaller lancets with a power of three hundred and fifty 

 diameters, that they are not piercing organs, but bear a 

 very delicate series of fine hairs on the tip (small circle 

 on fig. 3). 



The hind leg (fig. 4) is truly remarkable ; the process 

 of blunt knobs or teeth on the femur, and of bent 



Fig. 5. — End of tibia, and part 

 of tarsi of middle leg, of S. pipiens. 

 ■ X 94 diameters. 



Fig. 6.— End of tibia of 

 fore leg of 5. pipiens. x 125 

 diameters. 



spines on the tibia, are contrived to lock on to each 

 other and so constitute a sort of pincer. From its ex- 

 traordinary elaboration and powerful construction it 

 must play an important part in the insect's life-history ; 

 it is probably used in crushing some kind of capsule or 

 part of a flower to admit of the pollen being extracted. 

 By careful focussing with a power of three hundred 

 and fifty diametei's, some minute trachse may be de- 



tected above the knobj on the femur (small circle, 

 fig. 4.) 



It is possible that the spines on the tibia may be 

 capable of erection, as there appears to be some trace 

 of a muscle underneath them. Of the uses of the setae 

 on the middle and fore legs it is difiicult to form an 

 idea ; they may be the remnant of former useful 

 appendages, the insect having changed its manner of 

 obtaining food, but from their very marked character 

 and the modification which in that case has taken place 

 in the lancets, leaving them unmodified, this is very im- 

 probable ; besides, the spines at the end of the tibia of 

 the fore leg are found in most, if not all, of the 

 Syrphidje.* 



An antenna is shown in fig. 7. It resembles Syrphus 

 balteatus and others of the family; the small circular 

 markings are probably olfactory organs, and would be 

 of service to a flower-feeding insect; at a deeper focus 

 there is a curious organ of a rather vermifoiTU appear- 

 ance, which seems to be for the same purpose. The 

 male organs are very interesting, and can seldom be so 

 well seen as in this fly — though even here it is far from 

 easy to make a satisfactory diagram (fig. 8); two large 

 feeling organs, two " claspers " (fig. 9), and two inner 

 " holding organs " (fig. 10), as well as a seminal duct, 

 are all clearly seen, but other parts are very nebulous, 



Fio. 7. — Antenna of S. 

 pipiens. x .50 diameters. 



Fig. 8. — Diagram of the hypopygiimi 

 of S. pipiens. 



overlap, and difficult to differentiate. The apparatus 

 shown in fig. 10 is a very pretty microscopic object, 

 and with the " claspers " (fig. 9) (note how the setse are 

 turned back so as to form hooks) and the process on 

 the coxse of the hind leg, are claviously all modified 

 with the object i f accentuating the male's firm hold of 

 the female. The remarkable elaboration and com- 

 plexity of detail ou this minute fly (the female is § of 

 an inch long, the ni le a little less), cannot fail to 

 strike an observer. It is interesting to compare this 

 insect with another nearly related to it. Ascia podgrica 

 is rather smaller, and the abdomen very different in 

 shape, being a pointed oval tapering with a curve to 

 the base, but the wings, the fore legs, and the moutn 

 organs are identical ; the femur of the hind legs is 

 thickened in precisely the same manner, but it is 

 toothed with sharp setse, and there are no spines on 

 the tibia, the edge being hardened and chitinous in- 

 stead ; the middle legs lack the elaborate spines, 

 and the autennse are slightly different in shape. 

 Erystalis pertiuax and Heliophilus trivittatus carry a 



* I have had an opportunitv of watching, at all events, one of the 

 uses of the hind leg; a female extended her long membranous 

 ovipositor and drew it very carefully through the teeth of the femur 

 and tibia, which were compressed for the purpose ; this was repeated 

 many times. T am inclined to think that the nimierous hairs and 

 spines on the legs are primarily intended for cleaning purposes. 



