n the
Amblypygi, or with the posterior pair, rarely the anterior pair as
well, replaced by tracheal tubes. Intromittent organ of male in the
apical segment of the 2nd prosomatic appendage.

[Illustration: FIG. 61.--_Liphistius desultor_. Ventral view with the
prosomatic appendages cut short excepting the chelicerae (i) whose
sharp retroverts are seen. Between the bases of the prosomatic limbs
an anterior and a posterior sternal plate (black) are seen. 1, The
sternum of the first opisthosomatic or genital somite covering the
genital aperture and the first pair of lung-sacs. In front of it the
narrow waist is formed by the soft sternal area of the praegenital
somite; 2, the sternite of the second opisthosomatic somite covering
the posterior pair of lung-sacs; 3 and 4, the spinning appendages
(limbs) of the opisthosoma; a, inner, b, outer ramus of the appendage;
ii, sternite of the eleventh somite of the opisthosoma: in front of it
other rudimentary sternites; an, anus.

(Original as above.)]

Sub-order a. Mesothelae (see figs. 60 to 62).--Opisthosoma distinctly
segmented, furnished with 11 tergal plates, as in the Amblypygi; the
ventral surface of the 1st and 2nd somites with large sternal plates,
covering the genital aperture and the two pairs of pulmonary sacs, the
sternal plates from the 6th to the 11th somites represented by
integumental ridges, weakly chitinized in the middle. The two pairs of
spinning appendages retain their primitive position in the middle of
the lower surface of the opisthosoma far in advance of the anus on the
3rd and 4th somites, each appendage consisting of a stout,
many-jointed outer branch and a slender, unsegmented inner branch.
Prosoma as in the Mygalomorphae, except that the mesosternal area is
long and narrow.

Family--Liphistiidae (_Liphistius_, *_Arthrolycosa_).

Sub-order b. Opisthothelae (see fig. 63).--Opisthosoma without trace
of separate terga and sterna, the segmentation merely represented
posteriorly by slight integumental folds and the sterna of the 1st and
2nd somites by the opercular plates of the pulmonary sacs. The
spinning appendages migrate to the posterior end of the opisthosoma
and take up a position close to the anus; the inner branches of the
anterior pair either atrophy or are represented homogenetically by a
plate, the cribellum, or by an undivided membranous lobe, the colulus.

Trib