32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



tunately since it has no relation to ecdysis. The corpus allatum 

 hormone has been supposed to operate entirely by inhibiting adult 

 development, but more recent investigations indicate that it actively 

 affects the larva. The immature insect grows between moults and may 

 undergo slight or considerable changes at the moults. Hence, Wiggles- 

 worth (1959) has pointed out that "the hypothesis that this hormone 

 merely inhibits differentiation toward the adult becomes untenable." 

 Further, he says, "the corpus allatum hormone is clearly doing some- 

 thing active and positive in causing differential growth of larval type." 

 A review of the structure and function of the endocrine glands of 

 Lepidoptera has been given by Hinton (1951). 



While most of the adult development either is somehow inhibited 

 in the larva, or the thoracic-gland hormone is not always secreted in 

 sufficient amount, some adult structures do develop from an early 

 stage in the larva. A striking example is that described by Eassa 

 (1953) of the growth of the adult antennae and mouth parts in the 

 larval stages of Pieris brassicae. The adult antenna begins its develop- 

 ment in the first larval instar as a thickening of the epidermis beneath 

 the larval organ. As the antennal rudiment enlarges, the epidermis 

 folds inward as a containing peripodal pocket. During the following 

 instars the base of the antenna moves upward beneath the larval 

 cuticle until it reaches the position of the adult organ on the face. The 

 peripodal pocket likewise elongates, but as an open slit, and finally 

 it opens out so as to free the antenna, still beneath the larval cuticle. 

 The everted wall of the pocket becomes the imaginal epidermis of the 

 head between the adult and the larval antennae. 



Likewise, as shown by Eassa, the rudiments of the adult maxillae 

 appear in the first larval instar as thickening of the epidermis beneath 

 the larval maxillae. Through the following instars they develop within 

 pockets of the epidermis. The galeae grow to such an extent that they 

 become wrinkled, and when everted in the early pupal stage they are 

 long and folded upon themselves. The larval mandibles shrink to the 

 vestigial organs of the adult. The imaginal labium develops mostly 

 during the fifth larval instar. 



It is well known that the invaginated leg and wing buds of most 

 holometabolous insects develop during the larval stage. In some of 

 the nematocerous Diptera they are evaginated beneath the larval 

 cuticle in the last larval instar, as the writer (1959) has noted in 

 the mosquito. 



The postembryonic development of the internal reproductive organs 

 of the psychid lepidopteron Solenobia triquetrella is described by 

 Ammann (1954) and by Brunold (1957). Rudiments of the testes 



