188 AN ESSAY ON THE DEVELOPMENT 
an almost complete hood over the lacinia. This is well illustrated in the maxilla of the 
oriental cockroach, Periplaneta orientalis, shown at Pl. ILI, Fig. 8. At this point a 
comparison of the figure just cited with the galea of Simulium (PI. I, Fig. 1*) will 
prove interesting and instructive. 
In the Hymenoptera the galea dominate throughout ; no elongated palpifer is ever 
developed, and indeed the maxillary palpi are sometimes almost rudimentary in the 
Apide, as shown at Pl. III, Fig. 15. 
In Polistes, illustrated at Pl. II, Fig. 18°, we find a common type of the Vespide, 
where the lacinia forms a small, blade-like structure, free for almost its entire length, 
and the maxille as a whole shelter a large part of the labium. In those cases in which 
the “ maxille ” are elongated, the galea is usually the organ affected. 
Thus in many Meloids among the Coleoptera we have the mouth parts elongated, 
and a study of the maxilla of Memognatha (PI. III, Fig. 20) shows at once the scler- 
ites concerned. Here the lacinia is much reduced, and if we remove it altogether we 
have the normal Lepidopterous maxilla, which tends to a locking together to form a 
complete tube. Recently it has been found that in certain Lepidoptera the lacinia are 
actually present, and the figures which I have seen indicate a structure in all essentials 
like that of Nemognatha. 
While speaking of the Lepidoptera it may be well to cite Pronuba (PI. III, Fig. 
21), in which the palpifer is elongated in the female and highly specialized into a sen- 
sory and tactile structure, though unjointed. In a well-prepared specimen the point of 
origin is perfectly clear, and it is entirely homologous with the structure seen in Bitta- 
cus. In the male (Pl. III, Fig. 19) the “tentacle” is not developed, though the 
palpifer is enlarged to some extent. 
In the Apide, among the Hymenoptera, the lacinia disappear entirely in extreme 
cases, or are at least greatly reduced, while as already stated the palpi are sometimes 
scarcely visible. The galea, on the other hand, is very prominently developed, and 
when at rest envelopes the ligula and paraglossze almost completely. In Pl. III, Fig. 
15, is represented the usual appearance of all the parts separated, while at Pl. II, Fig. 
15", the transverse section of the mouth structures of Xenoglossa pruinosa shows their 
normal relation when at rest. It is seen that the galea actually overlap somewhat at 
one margin, and a union along this line would be scarcely considered a violent stretch 
of the range of variation. Assume such a union, eliminate the paraglosse which are 
organs tending to obsolescence, and then compare with the transection of Hristalis 
tenax (Pl. I, Fig. 38"). If the palpifer be eliminated from this latter figure the cuts are 
practically identical. 
Returning to our figure of Bombus (Pl. II, Fig. 15), we note at the outer edges 
