90 Messrs. C. B. Williams and P. A. Buxton 



on 



emergence. It is probable that the young larva moves 

 along the passage by a series of telescopic expansions and 

 contractions of the abdomen, rather than by a simple 

 wriggling movement as de Saussure seems to imply in the 

 remarks quoted above. 



It is important to notice that the legs and antennae 

 of the first-stage larva are free from the body, and that 

 the skin, which is soon to be cast, envelops each limb 

 separately. Several observers have made the mistaken 

 observation that the skin enclosed the animal as a whole, 

 pressing the legs and antennae against the body. They 

 have assumed this from an examination of cast skins, in 

 which the envelope of each leg becomes completely tele- 

 scoped upon the base on the withdrawal of the leg, and is 

 not obvious in a cursory examination. On Plate VIII are 

 shown two microphotographs of a cast skin. In one the 

 skins of the legs and antennae remain telescoped as left 

 by the larva, and are very inconspicuous ; in the second the 

 leg skins have been drawn out before the specimen was 

 mounted. 



There has been much controversy as to the morpho- 

 logical status of this first skin, which is cast almost immedi- 

 ately after emergence. Most authorities have persisted in 

 regarding it as an amnion, being misled by the idea which 

 we have just corrected, that it encloses the whole insect 

 like an eggshell, and also by Brongniart's statement that 

 no spines are present on its surface. Pagenstecher's figure 

 (1864, PI. I) which showed these, and which is the best 

 figure of the cast skin yet published, has even been desig- 

 nated as " fanciful " by Packard (1898, p. 584). However, 

 in view of the observations stated above— namely, that it 

 has a number of spines on the abdominal and thoracic 

 tergites ; that it envelops individually the limbs and the 

 antennae ; and that the threads from the end of the 

 abdomen pass through it, and, further, from the fact that it 

 is resistant to boiling in potassium hydroxide, and that its 

 staining properties are similar to those of chitin — we have 

 no doubt that it is a true skin and not an amnion. 



Six and a half minutes after the first appearance of the 

 larva the skin split mid-dorsally, and three minutes later 

 the larva was completely free and fell soft and helpless to 

 the ground. The limbs left the skin after most of the 

 trunk was free; first the anterior pair, and then the two 

 posterior pairs and the antennae almost simultaneously. 



