180 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
the emergence of the fly as it does in Culex. I have observed 
the liberation of the imago of Chironomus only. Here a large 
amount of air is admitted under the skin, so that the pupa has a 
glassy appearance, the preliminary movements are prolonged and 
violent, and the imago becomes markedly displaced in relation to 
the pupal parts. The apex of the abdomen, for example, finally 
lies three joints cephalad of its own sheath. In one species studied, 
the small apple-green fly emerges so rapidly that it takes wing with¬ 
in fifteen or twenty seconds from the moment when the pupal cuti¬ 
cle first ruptures. Comparing this with the slow emergence of 
Culex leads me to think that a connection exists between the rapid¬ 
ity of the emergence, the amount of air admitted beneath the cu¬ 
ticle, and the relative displacement of the imago in relation to the 
pupal sheaths. 
The mouthparts .—The mouthparts of the pupa develop during 
the last laiwal instar. The two organs that arise from invaginate 
imaginal buds, the labium (pi. 15, figs. 32, 34, li) and the maxillary 
palpus (pi. 15, fig. 29, maxp bd), appear first. The development of 
the labial bud may be taken as typical as regards the histological 
changes. The dermis beneath the labial sclerite thickens and pro¬ 
liferates, until a plate of minute cells, which stain deeply with haema- 
toxylin, is formed. While steadily growing upward, this plate is 
depressed and finally the bud consists of a bipartite eminence aris¬ 
ing from the floor of a deep pocket. Both pouch and eminence 
secrete a delicate cuticle. The labial imaginal buds of Chironomus, 
Anopheles, and Corethra closely resemble the bud in Culex and a 
similar double structure has been described for the Pupiparous fiv, 
Melophagus (Pratt, ’93) . Later in the instar than the labial and 
palp buds, the dermis of the top of the head thickens, stains deeply 
with haematoxylin and grows out as a cylindrical pouch. This bud 
forms the labrum (pi. 15, fig. 32, la bd). It projects caudad, 
depresses the adjacent tissues and lies in a shallow mesial fur¬ 
row. Of slow growth until immediately before pupation, it then 
elongates rapidly, and reaches back to the origin of the epiphar¬ 
yngeal muscles (epi m) before the head cuticle splits. At the 
same time that this bud elongates, the cells of the hypodermis of the 
flabellae enlarge and show a marked affinity for “orange G.” The 
dermis then retracts, separating from the overlying cuticle. In 
terms of their dermis the flabellae are converted into shallow 
