NEW MALLOPHAGA. 2l3 



with tlie outer arms (tf the W-shaped sternum. Eacli 

 angle of this, again, is free from cliitin. Tlie kiteral 

 walls are thick and especially so at their bases, where 

 they are produced into a large, inward-projecting 

 ridge (b). The non-chitinization of the angles of the 

 sternum and of its union with the i)leural sclerites 

 makes it evident that it is formed to enlarge by a 

 diverging of the sides of the lower angles when an egg 

 passes into the genital chamber. The inner lining (ci) 

 of the latter is thin but mostly cliitinized. A large mass 

 of transverse muscles (tm) surround the inner wall, Ijeing 

 attached latterly to the walls of the sternum and their 

 enlarged bases. Back of the vaginal opening their 

 inner ends are attached to a longitudinal dorsal crest of 

 the inner wall of the cavity. A few longitudinal mus- 

 cles (Im) also are present. 



The genital cavity is wide posteriorly but becomes 

 narrower in front. It is almost divided into two longi- 

 tudinal chambers by the dorsal ridge of the ventral 

 groove of the sternum. The vagina opens into its ante- 

 rior end somewhat to the right. This is a large tube 

 and must be regarded as a part of the exterior since it 

 possesses a chitinous intima continuous through that 

 of the genital cavity with the exterior covering of the 

 body. From the genital chamber the vagina (plate 

 xvii, figs. 2-5, vo, av, pv, and ( ') runs a short 

 distance dorsally and then turns forward. It forms 

 a large U-shaped tube (plate xvi, fig. 3, ra) lying 

 in the ventral part of the abdominal eavity. with the 

 closed end reaching far forward. Sometimes it is some- 

 what spirally twisted upon itself. The anteriorly run- 

 ning arm begins at the anterior end of the genital 

 cavity to the right of the other backward running 

 arm (plate xvii. figs. 2, 3. 4, ro, av, pv). The latter is 



