26 MOSQUITOES OF NORTH AMERICA 
be any modification of the chitin overlying them, and of course there is no trace 
of the “rod and cone” structure of the compound eyes. We shall revert to 
these vestigial eyes again in our discussion of the eyes of the larva. 
THE ANTENN-. 
The antenne are composed of fifteen segments. The basal segment is greatly 
reduced and not distinctly visible, and therefore in descriptive work the antennx 
are considered as fourteen-jointed. 
Child, who demonstrated the presence of the basal rudimentary segment, 
states that the antenna is made up of sixteen elements, but he was in error with 
the number of joints in the shaft. In all Culicide examined by us the number 
of antennal joints, both in the male and female, have been found the same, 
fifteen, if one counts the basal reduced joint. The second joint differs from all 
the others; it is large, globose, with a cup-shaped hollow on top, and upon the 
floor of this hollow the third joint is inserted. In descriptive work this joint is 
usually termed the torus. This joint constitutes a highly specialized sense- 
organ, generally accepted to be an organ for the perception of sound waves. 
Farther on we will give the details of structure of this organ and a discussion 
of its functions. The joint differs considerably in size in different species and 
in the two sexes. The torus is largest in the male and this sexual difference is 
most marked in those species in which the male antenne are strongly plumose. 
The tori are usually naked and smooth; often they are pruinose and sometimes 
more or less densely clothed with scales; there may be small scattered hairs 
present upon the surface. 
The outer thirteen joints constitute the shaft and are slender, more or less 
elongate, and cylindrical ; they are more or less pubescent and each bears a whorl 
of hairs. The appearance of the shaft, and the details of structure of the com- 
ponent joints, differ considerably with the species and groups of species and 
particularly in the two sexes. 
The simplest form, perhaps, is that which obtains in the females of Culez, 
Aédes, Anopheles, and related forms. In these the joints are elongate, cylindri- 
cal, subequal, with a whorl of long hairs at the base; the fourth joint (the second 
of the shaft) is the shortest, each succeeding joint progressively longer. The 
first and the last joints of the shaft differ most from the others. The first joint 
of the shaft is longer than the succeeding ones and usually more or less swollen; 
it also differs from the others in lacking the basal whorl of hairs and bears in- 
stead some irregularly inserted hairs near its middle. The terminal joint is the 
longest of the series and has a pointed apex; besides the basal whorl it has a 
whorl of sparse hairs just below the tip. 
In some forms there is an apical whorl of smaller hairs upon all the joints of 
the shaft, but these do not show the regularity of insertion of the basal whorl 
of hairs. Besides these coarse hairs of the whorls there are many fine hairs, in- 
serted in sensory pits, scattered irregularly over the surface of the joints; they 
vary in coarseness and abundance with the species. In addition scales may be 
present on some of the joints—particularly the first joint of the shaft is some- 
