MOEPHOLOGT OF THE PEDIPALPI. 47 



admitted tlTat tracheae have been formed from lun^-books twice 

 at least withiu the limits of the Arachnida. As I have already 

 pointed out, any attempt to derive lung-books from tracheae lands 

 one in an equally awkward position. The three remaining 

 orders — Phalangids, Pseudoscorpions, and Solifugse — are unfor- 

 tunately the three about whose morphology we know least. They 

 seem absolutely marked off from each other — the Phalangidse by 

 their extraordinary reproductive apparatus ; the Solifugse by the 

 segmentation of the carapace and the presence of thoracic stig- 

 mata ; and the Pseudoscorpions by the absence of both o£ these 

 sets. Por these reasons I have refrained from attempting to 

 construct a phylogenetic tree in this place, as it seems useless 

 to try any arrangement of the Lipoctena (Poeock) until more is 

 known both of their structure and development. 



EXPLANATION OF THE PLATES. 



Plate III. 



Fig. L ThelypJionus, opened from the dorsal surface. The superficial muscles 

 of the thorax have been removed, i.-vi., appendages ; c.o., caudal 

 oi'gan ; d.c.m., dorsal tail-muscle ; d.v.m.s., dorso-ventral muscle of 

 eighth free segment ; g, thoracic expansion of gut ; ht., heart ■ 

 O.C., central ejes. 



1 a. Portion of trabecular tissue from anterior lobe of gut. 



2. Transverse section of thorax of small Thclyphomis. cox., coxal gland ■ 



ent., entostermite ; g and g', diverticula of gut ; m.d.g., anterior 

 median diverticulum of gut ; ii.g., thoracic nerve-ganglion ; st., sto- 

 modgemn. 



2 a. Transverse section through stomodteum in front of fig. 2. 



3. Stercoral pocket and proctodaeum. 



4. Thorax after removal of the gut. c.c, cerebral ganglia; cox., coxal 



gland ; cox.d., duct of coxal gland ; cvt., entosternite. 



5. Cerebral and thoracic ganglia, iii.-vi., nerves to appendages; oc, 



optic nerves ; oes., oesophagus. 



6. Posterior portion of abdomen after removal of gut and digestive 



gland, n.g., nerve-ganglion; r., rectum; l.n.s. and r.s.s., left and 

 right sacs of stink-gland ; s.g., coiled tubes of stink-gland. 

 6 a. Section through part of waU of stink-sac. 



7. Section through caudal organ, cii,., cuticle; hy., hypodermis ; s.c. 



sense-cells. 



8. Anterior segments of abdomen. The anterior process of the second 



sclerite has been removed so as to open the genital vestibule, c^ and 

 C-, chitinous supports of the genital vestibule ; ge.v., genital vestibule • 

 lb.\ and lh.% first and second lung-books; se.t)., dilatation of vas 

 deferens ; x, hard structure in sb.v. 



