IM)IAX DRAdONFLlES. Aol 



The Imago (Plato 1.) 



The imaiTO is made up of a head, a prothorax furnished with a pair of 

 legs, a thorax furnished with two pairs of wings and legs, and lastly a 

 more or less elongatetl abdomen, the terminal segment of which is furnished 

 with one or two pairs of curious anal appendages. 



The Head of which the eyes form the greater part, is ordinarily and 

 relatively very large and is either globular or more or less, transversely 

 elongated. Posteriorly it is deeply cupped, the concavity being known as 

 the " occipital cavity " and here it articulates by means of two condyles, 

 with the prothorax, which latter structure projects so far into the 

 occipital cavity as often to be almost or completely hidden. The 

 condyles allow a very free movement of the head in almost any 

 direction. The eyes are two, large, compound organs made up of many 

 hexagonal facets, numbering in the larger species upwards to 20,000 

 in each eye. The facets are larger on the upper surface than they 

 are on the lower, an arrangement which affords the insect the 

 advantages of long and short sight, the latter being very necessary 

 in order that it may scan the surface over which it is flying. Another 

 factor which very materially assists the keen sight of these insects 

 is that the eyes are more deeply pigmented above than below. The qjqs 

 according to the species are contiguous across the middle line to a greater 

 or lesser extent or they may be slightly or widely separated. In Plate II, 

 fig. 1, the eyes of an Aeschnine are shown broadly contiguous, in fig, 6 

 the eyes of a Libelluline are sbnvn just touching : again in tig. 2, those 

 of a Gomphine are seen separated and lastly in fig. o the eyes of an 

 Agrionine are seen so widely separated as to appear as if stalked or pedi- 

 culated. This pediculation of the eyes is even more noticeable when 

 viewing the head from bene:xth as seen in fig. 4. 



According to the development of the eyes and their relation to one an- 

 other, depends the size of the ''occiput" or that part of the head lying 

 between and behind the eyes. In the Aeschnines and Libellulines it is 

 triangular and small : in the Gomphines and Agrionines it is quadrilateral 

 and relatively larger. Posteriorly it forms part of the rim of the occipital 

 cavity, the remaining portion of this lip being formed by the free margin 

 of the eyes and usually rounded, tuniid or sinuous. 



Between and in front of the eyes in the Anisopteridtc and in some of " 

 the Zygopteridis {Ithinocypha and Micronierus) will be seen a more or 

 less prominent eminence or tubercle which is known as the " vesicle."' In 

 the Libellulines this structure is somewhat triangular and cupped in front 

 and encloses the middle ocellus, one of three accessory eyes known as 

 " ocelli." In some of the night-flying Odonata the vesicle overhangs the 

 middle ocellus to such an extent as to suggest the hood of a motor-lamp 

 and may materially assist the function of sight. The ocelli are small, oval 

 or rounded, polished bodies placed about the vesicle in a triangle in some 

 genera or in a transverse straight line in others. In juxta-position to the 

 outer ocelli, are situated the antennte, slim, short and comparatively incon- 

 spicuous and formed of two moderately robust basal segments and four 

 longer and finer terminal segments, the distal one being pointed. (Never 

 clubbed as in the Ascalaphinte which are sometimes mistaken for Dragon- 

 flies.) The antennje are often scantily furnished with stiff, minute hairs. 



The fore part of the head consists of a broad, angulated plate, the 

 "clypeus", which is divided by a suture crossing its upper part into the 

 " front " or part above the suture, and the " epistome " (Plate II, figs. 1, 2 

 and 6) or the part below it, from which is suspended the upper lip or 

 " labrum ". The front presents a sharply angulated or rounded border 

 in its upper part, which is usually more or less, deeply notched. (Anisop- 



