4 BRITISH LEPIDOPTERA. 



whilst the form and appearance of the larva at hatching is known as 

 the first "instar," that of the larva after its first moult as the second 

 instar, and so on. 



We are now in a position to discuss the nature of the larval ecdyses. 

 The larval skin is composed of a cellular layer or hypodermis situated 

 on a basement membrane. The hypodermis consists of chitinogenous 

 cells, and these excrete a substance which remains attached to the 

 body and forms the hard outer layer of the larval skin. This layer of 

 chitin has no vitality, it varies much in thickness and in its general 

 character, and Krawkow considers it to be of a somewhat variable 

 chemical composition. It is, however, composed largely of nitrogen 

 and carbon, and hence its formation has been suggested as a means of 

 getting rid of a great deal of the nitrogenous and carbonaceous matter 

 from the blood. 



The observations of Trouvelot on Telea polypliemus show that the 

 increase of size and the rapidity of growth in some phytophagous larvae 

 are enormous. He states that the larva of this species weighs when 

 hatched -^ of a grain, in 10 days it weighs ^ a grain, in 20 days 3 

 grains, in 30 clays 31 grains, in 40 days 90 grains, in 50 days 207 

 grains, i.e., it has increased to 4,140 times its original weight. During 

 this time it will have eaten 86,000 times its primitive weight of food. 

 Of this about one quarter of a pound becomes excrementitious matter, 

 207 grains are assimilated, and over 5 ounces have evaporated. 

 Dandolo gives the weight of the larva of Bombyx mori on hatching as 

 3-^q of a grain, and when fully grown as 95 grains, so that during 

 this time the larva has increased to 9,500 times its original weight, and 

 to do this it has eaten 60,000 times its original weight of food. New- 

 port found that the larva of Sphinx ligustri increased from -^ of a grain 

 on hatching to nearly 125 grains (fullfed, 32 days after), an increase of 

 9,976 times its original weight ; whilst Lyonet asserts that the larva 

 of Cossus ligniperda increases between hatching and maturity 72,000 

 times its original weight. Newport adds that those larva? in which 

 the proportion of increase is the greatest, are usually those which 

 remain longest in the pupal stage. This we very much doubt, e.g., 

 ( 'ossus ligniperda exists for three years in the larval, and little more 

 than three weeks in the pupal, stage. He asserts, too, that growth is 

 most rapid after the last moult, and that a larva of Sphinx ligustri 

 increased from 20 grains to 120 grains during its last stadium, extend- 

 ing over eight days. The general principle here involved we believe 

 to be absolutely correct. 



We have quoted the above at length simply to show that lepi- 

 dopterous larvae must get rid of a large amount of waste material, as 

 the result of the vital activities, and it has been stated by Sharp and 

 others that it is for the purpose of getting rid of certain nitrogenous 

 waste matters that exuviation takes place. Certainly moulting in- 

 creases the size of an insect, but this appears to be only a factor of 

 secondary importance, for the integument can increase and stretch to 

 an enormous extent even at the moulting period, and many moults 

 are made when increase of size does not demand them, and the 

 shedding of the skin at pupation is accompanied by a decrease of size. 

 Chapman, however, expresses doubt as to exuviation having for its 

 object the getting rid of effete nitrogenous matters. He considers that 

 the larva does this in the ordinary way, viz., as uric acid, urates, and 



