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 orieatalis, shown at PL III, Fig. 8. At this point a 

 comparison of the figure ju<t cited with the galea of Simulium (PI. I, Fig. 1") will 

 prove intere^ting and instructive. 



In the Hymenoptera the galea dominate throughout ; no elongated palpifer i< ever 

 developed, and indeed the maxillary palpi are sometimes almo-t rudimentaiy in the 

 Apidfe, as shown at PL III, Fig. 15. 



In Folistes, illustrated at PL II, Fig. 18\ we find a common type of the Vespidte, 

 Avhere the lacinia forms a small, blade-like structure, free for almost its entire length, 

 and the maxillje as a whole shelter a large part of the labium. In those cases in which 

 the " maxilhe " 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 Nemognatha (PL III, Fig. 20) shows at once the scler- 

 ites concerned. Here the lacinia is much i-educed, and if we remove it altogether we 

 have the normal Lepido[)terous 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 J^eviognatha. 



While speaking of the Lepidoptera it may be well to cite Pronuha (PL III, Fig. 

 21 ), in which the palpifer is elongated in the female and highly specialized into a sen- 

 sory and tactile structure, though mijointed. In a well-prepared specimen the point of 

 origin is perfectly clear, and it is entirely homologous with the structure seen in Bitla- 

 cus. In the male (PL III, Fig. 19) the " tentacle '' is not developed, though the 

 palpifer is enlarged to some extent. 



In the ApidiK, among the Hj'menoptera, 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 paraglossia 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 jiruinosa 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 paraglossie which are 

 organs tending to obsolescence, and then compare with the transection of ErMalis 

 tenax (PL I, Fig. 3 '). If the pal[)ifer be eliminated from this latter figure the cuts are 

 practically identical. 



Returning to our figure of Bomhus (PL III, Fig. 15), we note at the outer edges 



