THOMPSON: ANATOMY OF MOSQUITO. 
195 
says: “ Whether an organ, as wing, leg, antenna, or mouthpart, 
shall begin as an invagination or an evagination of the derm is 
chiefly a matter of mechanical necessity or ease and of the radical¬ 
ness of the metamorphosis.” The “ brain appendages ” of Musca, 
the deep cephalic pouches of Chironomus, the shallow cephalic 
pouches of Simulium, and the independent eye and antennal for¬ 
mation of Culex do not constitute a closely locked series. The 
character and position of the invagination differ in each instance. 
The genera can be compared only with respect to the radicalness 
of the metamorphosis in each case, by which varied modifications 
of tendencies that exist throughout the Diptera are presented. That 
mechanical necessities are more potent than relationship in deter¬ 
mining the character of a bud is well shown by a comparison of the 
antennal buds of Culex, Anopheles, and Corethra. The larva of the 
first genus has a broad, capacious head, but the head of the larva 
of Anopheles is laterally compressed, and that of the Corethra larva 
is markedly flattened from side to side. The antennal buds in Culex 
are thrust back into the cavity of the head. In the other genera 
the antennal buds are thrust back in deep longitudinal furrows on 
either side of the head, and the invagination pocket is narrowly 
open for its entire length. 
Summary. 
The alimentary canal of the mosquito has a midgut and hind gut 
which are not subdivided into numerous or well defined regions, but 
the fore gut exhibits the maximum amount of differentiation that has 
been found among the flies. It may be divided into proboscis canal, 
pharynx, antlia, and esophagus. The pharynx and antlia are pump¬ 
ing organs. Their suctorial action depends on the modification of 
the chitinous intima to form definite areas or “plates,” which spring 
inward and occlude the lumen, to be withdrawn again by muscles. 
This duplication of the pumping apparatus places the mosquitoes in 
the diantlial class of flies, a group which probably includes all the 
Nematocera. The Muscidae and others of the Cyclorrhapha are 
monantlial, having only the anterior or pharyngeal pump. There is 
no secondary union of the pharynx with the walls of the head, so that 
it is not converted into a fulcrum. In this region, as is the case 
