150 BUTTERFLIES AND MOTHS 



which shrivels and dissolves away under the influence of heat. 

 Beneath this hard external epidermis composed of chitine we 

 find the true skin, forming a deep, soft layer, and intimately con- 

 nected with the external epidermis ; the minute ducts of numer- 

 ous small glands embedded in the true skin pass to the epidermis, 

 entering the base of the external hairs. According to the age 

 and progress of development of the insect, certain calcareous 

 salts, colouring matters and fat are found to be added in varying 

 proportions to the chitine of the outer integument, and it is this 

 external epidermis which from time to time is cast or moulted 

 off during the growth and transformation of the insect. 



"The external skin of insects may be smooth and glossy in 

 appearance, covered with raised, warty knobs, or clothed with 

 hairs or scales. 



"The body of a true insect, such as a beetle, a L butterfly, or a 

 caterpillar, is divided into three parts viz. the head, consisting 

 of a number of closely united segments, bearing on its lower or 

 ventral surface the mouth, and upon its sides two large compound 

 eyes. Upon its upper or dorsal surface, in many species of insects, 

 are one, two, or three simple eyes, or ocelli, and a pair of feelers 

 or horns, the antenna. The second division of the insect's body 

 is called the thorax, or chest region, and consists of three segments, 

 which are either separate from each other or fused together. 

 Each of these segments has a distinguishing name : the first, which 

 joins the head, is called the prothorax, and bears the front or 

 anterior pair of legs ; the second is the mesothorax, and, in the 

 case of a winged insect, carries, besides the pair of legs on the 

 lower surface, a pair of wings upon the upper or dorsal surface ; 

 the third segment, called the metathorax, may also carry a pair 

 of wings on its dorsal surface as well as the regulation pair of legs 

 beneath. 



"The third division of the insect's body is called the abdomen, 

 and is composed of a series of segments varying in number. In 

 the perfect or adult insect no legs are to be found upon the abdomen, 

 but during the larval stage of the insect's life fleshy tubercles, 

 the pro-legs, may be present. The six true legs of the insect are 

 always placed upon the ventral surface of the three thoracic 

 segments ; while the pro-legs, which are only present on the larvae, 

 are in pairs upon the lower surface of the abdominal segments. 





