A somite placed between the prosoma and mesosoma - the prae-genital somite - appears to have belonged originally to the prosomatic series (which with its ocular prosthomere and palpi FIG.
In the female of Culex the palpi are much shorter than the proboscis; in Anopheles they are of the same length.
In the Argasidae the anterior portion of the dorsal surface of the body is extended forwards above the capitulum, so that this structure is concealed from above; the integument is fairly uniformly granular or coriaceous above and below; the palpi are simple and unmodified; there is no sucker beneath the claws in the adult, and there is only a slight structural difference between the sexes.
The palpi and probe or hypostome are attached to a movable sclerite or horny plate called the capitulum.
Maxillary and labial palpi are also present, and the latter, together with the labrum or lower lip, form the rostrum.
In the Ixodidae the capitulum is not overlapped by a forward extension of the dorsal area, which is smooth and firmly chitinized either in front or all over; the palpi are usually modified, that is to say, their second and third segments are usually excavated internally to form a sheath for the hypostome; there is a distinct sucker beneath the claws and the difference between the sexes is well marked, the males having the dorsal integument thickly and continuously chitinized, whereas in the females only its anterior portion bears a chitinous plate, the rest of the integument being soft to admit of its distension by the blood which is imbibed in quantity by members of this sex.
The bestknown family is the Hydrophilidae, in which the feelers are short with less than eleven segments and the maxillary palpi very long.
The old genus Anopheles (characterized by the palpi being long in both sexes) is now divided into a number of genera according to the character and shape of the scales on the different regions of the body and on the wings.