a 



COMPOSITION OF THE HEAD IN HYMENOPTERA 55 



The composition of the head in the Hymenoptera. Batzeburg stated 

 in lx;>2 that the head in the adult Hymenoptera (Cynips, Hemiteles, 

 and Formica) does not correspond to that of the larva, but is derived 

 from the head and the first thoracic segment of the larva. West- 

 wood and also Goureau made less complete but similar observations, 

 though AVestwood afterwards changed his opinion, and the same 

 view was maintained by Reinhard. Our own observations (as seen 

 in Fig. 38) led us to suppose that this was a mistaken view ; that 

 the larval head, being too small to contain that of the semipupa, was 

 simply pushed forward, as in caterpillars. Bugnion, however, re- 

 affirms it in such a detailed way that we reproduce his account. He 

 maintains that the 

 views of Ratzeburg 

 are exact and easy to 

 verify in the chalcid 

 genus Encyrtus, ex- 

 cept, however, that 

 w r hich concerns the 

 ventral part and the 

 posterior border of 

 the prothoracic seg- 

 ment. 



As the time of 

 transformation ap- 

 proaches, the head of 

 the larva, he says, is 



depressed and SOOn FIG. 38. Larva (</) of a chalcid, about to pupate, with the 



head, including- the eyes and three ocelli, in the prothoracic seg- 



concealed under the ment . i, c, pupa, 

 edge of the protho- 

 racic segment ; the latter elongates, becomes thicker and more con- 

 vex, and within can be seen the two oculocephalic imaginal buds. 

 The head of the perfect insect is derived not only from the head of 

 the larva, but also from the portion of the prothoracic segment which 

 is occupied by the buds, i.e. almost its entire dorsolateral face. But 

 the hinder and ventral part of this segment (which contains the 

 imaginal buds of the first pair of legs) takes no part in the forma- 

 tion of the head ; these parts, according to Bugnion, towards the end 

 of the larval period detaching themselves so as to become fused with 

 the thorax and constitute the pronotum and the prosternum. 



This mode of formation of the head may be observed still more easily in 

 Rhodites, Hemiteles, and Microgaster, from the fact that their oculocephalic 



