576 



INSECTA. 



Agrion, Fabr., has the wings elevated perpendicularly in repose ; the head transverse, with the eyea apait ; v iie 

 form of the lower lip is similar to that of Jishna, but its middle lobe is slit to the base. The forehead is not fur- 

 nished with a vesicle ; the ocelli are nearly equal in size, and arranged in a triangle on the vertex ; the abdomen 

 is very slender and filiform, and occasionally very long. The body in the larva and pupa states is also long and 

 slender, and the abdomen terminated by two oar-like appendages ; the mask is flat, with the superior extremity of 

 the chin-piece elevated into a point in some, and forked in others. Libellula virgo, Linn., is of a golden-green 

 or bluish-green' colour, with the wings blue, either entirely or partially, and sometimes pale brownish-yellow. 

 [This and several other species of smaller size, belonging to the subgenera separated from Agrion by Leach, are 

 of very common occurrence in this country.] 



The other Subulicorn Neuroptera have the mouth entirely membranous or very soft, and com- 

 posed of parts very indistinct ; they have 5-jointed tarsi ; the lower wings are much smaller than the 

 superior, or even wanting ; and the abdomen is terminated by two or three long threads. They form 

 the genus 



Ephemera, Linn., — 



Thus named from the short duration of their life in the perfect state. The body is soft, long, slender, 

 and terminated behind by two or three long articulated filaments. The antennae are very small, and 

 composed of three joints, of which the last is very long, in the form of a conical thread. The front of 

 the head is advanced like a hood, often keeled and notched, and covers the mouth, of which we cannot 

 trace the organs on account of their softness and smallness. These insects cany their wings almost 

 always elevated perpendicularly, or but slightly deflexed, like the Agrions. The legs are very slender, 

 with the tibiae very short and united to the tarsi, which have often only four joints, the first being 

 nearly obsolete. The two ungues of the terminal joint are very compressed, and the fore-legs are much 

 longer than the others. 



The Ephemera: generally appear at sunset in the fine days of summer and autumn, along rivers, lakes, &c, and 

 sometimes in such numbers that the ground, after their death, is covered with them, so that they are carted away 

 as manure. The falling of one species, with white wings, resembles that of a fall of snow. 



These insects unite in swarms in the air, where they fly up and down, extending the threads of their tails. It is 

 there also that the sexes unite, the males being distinguished by two hooks at the extremity of the body ; their 

 fore-legs and anal threads are also longer, their eyes larger, and some males possess four eyes, two being much 

 larger, and elevated on columns. The females deposit their eggs in a gelatinous mass, and, as the propagation of 

 the species is the only object of the existence of the individual, they very soon perish, often on the day in which 

 they undergo the final change, sometimes living only a few hours. Those which fall on the water are greedily 

 seized by the fishes, and fishermen give them the name of Manna. But if we consider them in the larva state, 



we find their existence extending through two or 

 three years. In this, and the pupa state, they reside 

 in the water, concealed during the clay under stone-, 

 or in horizontal burrows, which they form in the 

 banks, from which it is supposed that these larvae 

 derive their food. Although resembling the perfect 

 insect in several respects, they differ materially in 

 having longer antennas, wanting ocelli ; by possess- 

 ing horn-like mandibles ; the abdomen has, more- 

 over, on each side, a row of plates, mostly in pairs, 

 which are a kind of false branchiae, and which are 

 employed not only in respiration, but also as paddles. 

 The pupa differs from the larva by possessing scales 

 inclosing the wings. At the moment when they un- 

 dergo this change they quit the water, and appear, 

 after casting their skin, under a new form ; but, by 

 a singular exception, they have to undergo another moulting before they are fit for propagation. Their last exuviae 

 are often found fixed to trees, and upon walls. 



De Geer formed these insects and the Phryganea into a distinct order, in consequence of the minuteness or 

 absence of the parts of the mouth. In the Tableau Elemewtaire of Cuvier they also form a peculiar group, named 

 Agnatha, but which formed part of the order Neuroptera. 



The number of the wings and of the anal filaments lead to the establishment of various divisions in the genus 

 Ephemera; some having four wings and two tails (E. Swammerdamiana) ; others four wings and three tails 

 (Ephemera proper, E. vulgata, Linn.) ; some with two wings and three tails, and the eyes of the male doubled, one 

 pair placed in foot stalks. [Others again have only two wings and two tails. These various groups have been 

 formed into separate genera by Leach, and other subsequent authors, E. vulgata, the commonest species, and 

 vbich is well known to fly-fishers under the name of the Grey Drake, being retained as the type of the restricted 

 genus Ephemera.] 



Fig. 106. — Ephemera vulgata : larva, pupa, and imago. 



