The " retrovert " or bent-back first pair of appendages is provided with a poison gland opening on the fang or terminal segment.
The second has for its pair of appendages the small pair of limbs which in all living Arachnids is either chelate or retrovert (as in spiders), and is known as the chelicerae.
- The plane of the articulation of the appendages of the 1st pair to the prosoma (the retrovert) vertical, the basal segment pro jecting straight forwards at its proximal end, the t raegcn - distal segment or fang closing backwards in a direction subparallel to the long axis of the body.
Hexapoda and Arachnida); the penultimate joint with a process equal in length to the last joint, so as to form a nipping organ (chelae of Crustaceans and Arachnids); the last joint reflected and movable on the penultimate, as the blade of a clasp-knife on its handle (the retrovert, After Lankester, Q.
Head tritognathous and diprosthomerous - that is to say, with two prosthomeres, the first bearing typical eyes, the second a pair of appendages reduced to a single ramus, which is in more primitive forms antenniform, in higher forms chelate or retrovert.