HYMENOPTERA CHAP. 



are passed through ; these, however, have not been followed out 

 in the case of any individual, and it is not possible to form any 

 final idea about them, but it seems probable that they are largely 

 changes of external shape, in conformity with the great changes 

 going on in the internal organs. Owing to the fragmentary 

 nature of observations, much obscurity and difference of opinion 

 have existed as to the metamorphosis of Aculeate Hymenoptera. 

 Sir S. Saunders gives the following statement as to the larva of 

 a wasp of the genus Psiliglossa? just before it assumes the pupal 

 form : " The respective segments, which are very distinctly indi- 

 cated, may be defined as follows : The five anterior, including 

 the head, are compactly welded together, and incapable of separate 

 action in the pseudo-pupa state ; the third, fourth, and fifth 

 bearing a spiracle on either side. The thoracical region termi- 

 nating here, the two anterior segments are assignable to the 

 development of the imago head, as pointed out by Ratzeburg." 

 This inference is not, however, correct. We have seen that in 

 the perfect Insect of Petiolate Hymenoptera the first abdominal 

 segment is fixed to the thorax, and Saunders' statement is in- 

 teresting as showing that this assignment of parts already exists 

 in the larva, but it in no way proves that the head of the imago 

 is formed from the thorax of the larva. It has been stated 

 that the larvae of the Aculeata have a different number of seg- 

 ments according to the sex, but this also is incorrect. The 

 difference that exists in the perfect Insects in this respect is due 

 to the withdrawal of the terminal three segments to the interior 

 in the female, and of two only in the male. The larva consists 

 of fourteen segments, and we find this number distributed in the 

 female perfect Insect as follows : one constitutes the head, four 

 segments the thorax and propodeum, followed by six external seg- 

 ments of the restricted abdomen, and three for the internal structures 

 of the abdomen. This agrees with Forel's statement that in the 

 ants the sting is placed in a chamber formed by three segments. 

 The development of the sting of the common bee has been 

 studied by Dewitz. 2 It takes place in the last larval stage. 

 Although nothing of the organ is visible externally in the adult 

 larva, yet if such a larva be placed in spirit, there can be seen 

 within the skin certain small appendages on the ventral surface 

 of the penultimate and antepenultimate abdominal segments 

 1 Trans, ent. Soc. London, 1873, p. 408. " Zeitschr. wiss. Zool. xxv. 1875, p. 184. 



