20 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [BuU. I 



proper nomenclature. It is therefore important to note the "land- 

 marks" for the recognition of the parts of the skeleton as well 

 as to provide a means — with figures and general descriptions — 

 for the guidance of the beginner ; so that there may be no loss of | 

 time interpreting the English of a description, or confusion because 

 of a knowledge of similar parts in other insects. To aid in under- 

 standing descriptions, a glossary of terms is appended (p. 300). 

 In all descriptions the insect is regarded as in a natural position 

 with feet on the ground and body parallel to the surface. 



The body of all Odonata is divided into three main divisions, 

 known as head, thorax, and abdomen. Each division is in turn 

 composed of a number of rings or segments, more or less modified, 

 but homologous with the segments of its wormlike ancestors. The 

 external skeleton is provided with pigment and divided into 

 sclerites or plates that are similar in different families and sub- 

 orders. The lines separating the sclerites are called sutures. 



The Body Structure 

 Adult 



Head. — Surrounding the mouth opening are projections of the 

 body wall and appendages designed to aid in capturing other insects 

 and preparing them for its use. Just above the opening is found 

 a broad, emarginate piece known as the labrum, which is about 

 twice as broad as long. Above it is a fixed sclerite known as the 

 clypeus (Fig. 3, a). 



Above the clypeus and between the large compound eyes occupy- 

 ing the sides of the head is an area known as the front. It bears 

 the jointed appendages called antennae. The front extends to the 

 small ocelli or simple eyes and is usually bounded by a suture on 

 each side below the compound eyes. The epicranial suture extends 

 from the rear of the head to a joint just behind the ocelli where it 

 forks and extends laterad to the compound eyes. The posterior 

 surface of the head, on either side of the foramen or body opening, 

 is commonly known as the occiput, and contains three sclerites, 

 the occiput and two postgenae more or less fused. 



Below the mouth opening there is a hinged organ, the labium, 

 which in most individuals covers the entire lower surface of the 

 head. Beneath the labium (or above it when the head is in posi- 

 tion) are found the two maxillae, one on either side, and between 

 the tips of the latter is a circular pad, the hypopharynx. 



The compound eyes are always large, frequently contiguous 

 above, and they contain a large number of hexagonal facets, some- 

 times of two different sizes. The antennae vary in shape and also 

 in the number of segments, there being usually seven. In the 

 Odonata the labium is unique because of its large size and great 



