52 



TEXT-BOOK OF ENTOMOLOGY 



pr.m 



.ant 



md 



" Vorkiefersegment," and it may thus be termed the premandibular 

 segment. 



As early as 1870 Biitschli observed in the embryo of the honey 



bee the rudiments of what appeared to be a pair of appendages 



between the antennae and mandibles, but, judging by his figures, 



nearer to and more like the mandibles than the rudimentary an- 



A B tennae (Fig. 35) ; they 



seemed to him " al- 

 most like a pair of 

 inner antennae." 



" I find," he says, 

 "in no other insects 

 any indication of this 

 peculiar appendage, 

 which at the time of 



FIG. 35. Head of embryo of honey bee : B, a little later stage its greatest develop- 



than A. pr.m, premaudlbulftr segment; cl, clypeus; ant, an- , 



tenna ; mil. mandible; mx, first maxilla ; M.C', second maxilla; meilt attains a larger 



xn, spiracle. After Biitschli. ,1 ,, 



size than the antennae, 



and which, afterwards becoming less distinct, forms by fusion with 

 that on the other side a sort of larval lower lip. That this append- 

 age does not belong to the category of segmental appendages is 

 indicated by the site of its origin on the upper side of the primitive 

 band." (Zeitschr. wissen. Zool., xx, p. 538.) 



Grassi has also observed it in Apis, and regards it as the germ 

 of a first, but deciduous, pair of jaws. In the embryo of Hylotoma 

 Graber (Figs. 134, 135) found what he calls three pairs of " prean- 

 tennal projections," one of which he thinks corresponds to the "inner 

 antennas " of Biitschli. This subject needs further investigation. 



It thus appears that the procephalic lobes of the embryo of in- 

 sects, with the rudiments of the antennae, constitute the primitive 

 head, and perhaps correspond to the annelidan head, while gradu- 

 ally the antennal appendages were in the phylogenetic development 

 of the class fused with the two segments of the primary head. That 

 the second maxillary segment, the occiput, was the last to be added, 

 and at first somewhat corresponded in position to the poison-fangs 



adult. " Campodea is now the first example where these appendages are present in 

 the sexually mature insect and function as constituents of the completed mouth 

 parts. I propose for these hitherto overlooked structures the name of intercalary 

 lobes." They each form a slightly developed chitinous lobe covering a gap between 

 the base of the labium and the fused external lobe and palpus of the first maxilkc 

 (which are inclined near the labium) in place of the mandibles which have sunken 

 inward. Uzel also homologizes these appendages with two similar projections 

 (Hiicker) observed in the embryo of Geophilus by Zograf to be situated in front 

 of the mandibles. Heymons has also detected this segment in the embryo of Lepisma. 



