x INTRODUCTION. 



ably in different groups and families. The larva is provided with a very complete 

 digestive system, which consists of the following organs (see Plate I., fig. 9) : A, the 

 oesophagus ; D, the ventriculus ; F, the clavate intestine ; E, the ilium ; H, the colon ; 

 K, the biliary vessels ; and 0, the spinning vessels. These last open at a small orifice in 

 the labium termed the spinneret (fig. 2, 5). They supply the silken threads which are 

 employed by most larvae in constructing their cocoons, and which also serve in cases of 

 danger as a rapid means of retreat. Many larva-, which live on shrubs and trees, suddenly 

 lower themselves to the ground by means of one of these silken threads, and thus often 

 escape being devoured by insectivorous animals. 



The entire growth of the insect is accomplished during the larval condition, the 

 increase in size being frequently very rapid. Owing to this circumstance larva' are often 

 compelled to shed their skin, and in many species a very considerable alteration both in 

 the shape and colour takes place at each moult, or eedysis as it is sometimes termed. 



THE PUPA. 



The pupa of a Lepidopterous insect is completely encased in a chitinous 

 envelope. With the exception of a slight twirling of the abdominal segments it is 

 incapable of any motion. In the pupa of Micropteryx the mandibles and Labial palpi 

 are said to be functionally active, but this is a very exceptional though extremely 

 interesting case. In conjunction with other evidence it would appear to indicate that the 

 Lepidoptera originated from insects with active pupae. The number of free or movable 

 segments of pupa' varies considerably in different groups and genera, and by some 

 modern authors it is regarded as a character of much importance in the framing of their 

 classifications. The various organs of the perfect insect are distinctly marked out 

 on the otherwise uniform integument of the pupa. In some groups, notably the 

 Micropterygina, these organs are much more distinctly indicated than in others. 



II.— ANATOMY. 



THE PERFECT INSECT OP IMAGO. 

 In common with all other members of the class, the body of a Lepidopterous insect 

 consists of three main divisions : (1) the head, (-J) the thorax, and (3) the abdomen. 



THE HEAD. 



The front of the head is termed the face, the top the crown, the sides are nearly 

 entirely occupied by the compound eyes (Plate I., H^;. 11, AA), and the lower surface 

 by the organs of the mouth. 



The Eyes consist of a very large number of simple lenses arranged in the form of two 

 hemispheres, one on each side of the head. The ocelli, or simple eyes, are situated on 

 the crown, and are usually almost entirely covered by scales. 



The Antrim,*' are two jointed appendages attached to the top of the head above the 

 eyes. They vary very much in structure. The following are the terms used in 

 de i idling the different forms ol antenna 1 in the Lepidoptera : — 



1. Pectinated, when the joints have long processes like the teeth of a comb, [f 

 these are .a: one side only, the antenna; are iinipectinated; if on both sides, bipectinated. 

 (Plate I., lig. 20, bipectinated antenna of Nyctemera annulata.) 



■1. Dentate, when the joints are armed with slight pointed spines. 



