March, 1902.] 



KNOWLEDGE 



67 



use their long-wiiuloil family title. AVhile the Swifts are 

 for tlie most part soljerly coloiireil, the Micrujileri/ijid.-i' 

 are some of the most lu'illiant insects we possess, ami if 

 only they were mai,'nitied to the dimeusious of the Swifts, 

 they would be the admired of all observers. The ground 

 colour of the fore-wings is usually a deep shining golden 

 bronze, and this is crossed in some cases with bars of 

 polished purple or silver. Many of them are common 

 enough in early summer in llowers or on the leaves of 

 youug trees, but they are so small that they usually escape 

 notice, and a lens is necessary to make out fully their 

 beauties. Both these groups of insects possess this clasping 

 lolie, and though at one time placed far apart from one 

 another in systematic classification, they are now often 

 associated together because of this and other peculiarities, 

 and many entomologists believe that they represent the 

 most ancient and ]irimitive type of Lepuloptera to be 

 found throughoi;t the world: 



To observe the other method of linkage that prevails in 

 the Lepidoptera, almost any kind of moth may be used. 

 We might, for exam[)le, take such an insect as the Common 

 Yellow Underwing (Triiiliwiia proiiuha), a moih that is so 

 abundant as to be within the reach of everybody. Suppose 

 we take tiret of all a male specimen ; if we separate one of 

 the hind-wings we see ]>roceediug from a point very near 

 its place of articulation, a strong, stout, curved bristle 

 (Fig. 3, <(), which is delicately grooved throughout its 



^ 



Fig. 8. — Bight Hind-wing of Yellow Underwing. o, male; b, female. 



length, and ends in a finely drawn-out point. This is only 

 half the appaiutus, and to find the other part we must go 

 to the fore-wing. Here, attached to the first of the great 

 uervures that radiate over the surface of the wing, just 

 below the anterior boundary, and not far from its base, is 

 what looks like a sHrelLing or excrescence. To see its true 



Fio. -t. — Underside of Base of Right Pore-wing of Yellow 

 Underwing. a, male ; 4. female ; showing Retlaaeuluiii, r ; 

 Tiift of Scales, s. Magnilicd 2 diameters. 



form, it will be necessary to remove the scales with which 

 it is thickly covered ; a little brushing with a camel's hair 

 brush will easily do this, and then it appears as a longi- 

 tudinal flaj} or coil of 

 stoutish membrane pro- 

 jecting from the nervure, 

 and with its free end bent 

 under in such a way as to 

 leave a passage between 

 itself and the general sur- 

 face of the wing (Fig. 4, a) . 

 If we now examine the 

 moth with its wings in 

 position as if for flight, we 

 see that the bristle of the 



Fta. 5. — Uuderside of Left ^\'iug9 

 of Male Yellow Underwing, showing 

 Spine passing through Ketinaculuui. 



hind-wing passes through the loop on the fore-wing, like 

 a thread through the eye of a needle, and thus ti3e two 

 wings are linked together (Fig. 5). 

 Next let us take a female, and deal with it in the same 



way. We find now that instead of a single bristle there 

 are three somewhat weaker ones (Fig. o, h), one of which 

 is very line, and all are bent at a shar]ier angle than in 

 the male insect. When wo examine the fore-wing, wc 

 find that the loop-like retinaculum, as it is called, has 

 entirely disappeared, and instead of it we find a bunch of 

 scales pointing in the opposite direction, and s]iringiug, 

 not from the nervure before-mentioned, but from the next 

 one farther down the wing (Fig. 4, h). Examining the 

 wings in jiosition, we find that the cluster of bristles on 

 the hind-wing is thrust through and entangled in this 

 bunch of scales, and thus the two wings are held together 

 to some extent, but of course not so effectually as in the 

 male insect. 



Tlierc is a slight variation from this type in the day- 

 Hying Burnet moths. These brilliant insects, with their 

 glossy greenish-black fore-wings relieved by crimson spots 

 or streaks, and with crimson hiud-wings, form some of 

 the prettiest ornaments of our grassy hillsides as they fly 

 from flower to flower in the brightest sunshine. In place 

 of the customary loop on the fore-wing we find them 

 provided with a sort of pocket into which the tip of the 

 bristle is thrust. In the long-winged and swift-flying 

 Hawk-moths, which are for the most part crepuscular in 

 their habits, the linking apparatus reaches its highest 

 development, in accordance with the exceptional vigour 

 and speed of their flight. In the Poplar Hawk-moth, 

 however, which is the most sluggish of the group, the 

 apparatus is quite rudimentary, and this, again, is in 

 accordance with its habit of carrying its hind-wing, when 

 at rest, in such a way that its front margin projects 

 beyond the fore-wings, for this would obviously pi-event 

 the bristle, if it were present, from being passed through 

 the loop. 



There is another very curious variation iu a group of 

 small moths called " Pearls." One of the commonest of 

 these is a long-legged insect generally found amongst 

 nettles ; it has glossy yellowish-grey wings, marked with 

 wavy lines, and showing a certain amount of iridescence, 

 whence its common name " Mother of Pearl " {Botys 

 verticalis]. In this insect and its allies, the male imitates 

 the female in being destitute of the loop, and thrusting its 

 bristle into a tuft of scales. 



The difl'erence between the single spine of the male and 

 the gi'oup of spines which is characteristic of the female, is 

 more apparent than real. For if the male spine is closely 

 examined under the microscope, it is seen as before- 

 lucutioued to be distinctly furrowed, and a transverse 

 section shows that it is made of several spines which have 

 cM^lesced. Thus both arrangements consist of a group of 

 spines, which in the one case are compacted, and in the 

 other remain distinct. 



From this sexual difference one would be inclined to 

 argue that male moths would exhibit a power of flight 

 somewhat superior to that of their partners, and it is 

 certainly true, in some instances at least, that the females 

 are much more sluggish than the males, and when on the 

 wing fly more heavily ; but it can hardly be said that this 

 is generally the case in any marked degree, and even if it 

 were so, the greater weight of the body in the female 

 insect might be as effectual a cause of retardation as the 

 less close linkage of the wings. And further, iu a few 

 instances, such as the Drinker and Oak Egger moths and 

 their allies, the males of some of which are extraordinarily 

 active, flying with great force and speedeveniu hot sunshine, 

 the wing-links are altogether absent. In these cases, 

 however, the secondaries, by their great ilevelopment 

 anteriorly, considerably underlie the jirimarics, and thus no 

 doubt render the spine and loop arrangement unnecessary, 

 if not indeed, impracticable. 



