416 jme. h. m. beenaed on the 



Fig. 9. End of mid-gut of a fasting Rhax, jammed against the stercoral pocket {stp), thereby closing 

 the passage ; letters as before. 



10. Longitudinal section through the wall of mid-gut at the wide anterior portion (segments 2 and 



3 of fig. 1). Im, longitudinal muscles ; cm, circular muscles. The epithelial cells stand on 

 a membrane [m) thrown into folds by the contraction of the longitudinal muscles. The 

 epithelial cells of mid-gut are being traversed by strings of food-globules {fg). Average 

 length of cell 20 /i. 



11. Enlarged portion of fig. 8. mg, mid-gut cells, which near the junction with the hind-gut are 80 yx 



long and 3 to 4 /x thick ; long strings of food-globules traverse them, hg, chitin-lined hind- 

 gut secreted by long, thread-like cells which appear to change into a fine tesselated epithelium 

 covering the stercoral pocket. /?«, longitudinal muscles; tin, transverse muscles binding 

 the lateral canals together (fig. 7) ; sjj, spongy layer composed of fluid-passages, cells, and 

 coagulum ; tr, trachea ; cm, //«', the musculature proper of the mid-gut, a continuation 

 of the muscles shown in fig. 10. 



12. Diagram showing the primitive relations which existed between the diverticula of the alimentary 



canal [mgd), the dorso-ventral muscles [dv), the tracheal invaginations {tr) , and the heart (A) 

 with its ostia. The dotted lines on the right indicate the extent to which this primitive 

 condition is still traceable in three Arachnids, viz. Thebjphorms, Scorpio, and Galeudes ; 

 D, the position of the diaphragm. (N.B. This figure should have been on the next Plate.) 



Plate XXXIV. 



Figs. 1-5. Diagrams of the abdominal alimentary system. 1. Scorpio. 2. Thelyphonm. 3. Obisium. 

 4. Galeodes. 5. Hypothetical primitive arrangement with at least 7 pairs of diverticula from 

 which the former can be deduced. In Scorpio the two posterior pairs have been suppressed, 

 the fifth pair lengthening backward. In Galeodes all but the first pair have been suppressed, 

 this single pair stretching backward outside the dorso-ventral muscles. In Thelyphomis 4 or 

 5 pairs persist, the 4th or 5th (?) stretching back inside the dorso-ventral muscles and being 

 themselves constricted. This process has gone still further in the Pseudoscorpions, reaching 

 to the 2nd segment, the ' hind-gut' being coiled. 

 (J. Longitudinal section through the last chamber of the heart of a Rhax, passing through an ostium ; 

 VI, VII, sixth and seventh abdominal segments ; h, heart ; fc, large cells (?fat cells) ; v, the 

 posterior vein ; fl, flexible chitin of intersegmental membrane ; cm, muscle-fibres forming 

 the tunic of the heart, cut through. 



7. Ventral aspect of a portion of a heart, dissected out. cm, the circular muscle-fibres shown in 



section in last figure ; n, layer of single nerve-fibrils with spindle-shaped nuclei. 



8. Diagram of the circulation in the abdomen of Galeodes. The blood, entering the abdomen 



through the neural arch of the diaphragm, follows the mid-gut and nerve-strands in the 

 ventral sinus {vs), from this it escapes on both sides among the mass of digestive diverticula, 

 reaching the heart after circulating among them ; tr, tracheae near a pair of abdominal 

 stigmata; g, genital gland; h, heart [cf. Plate XXXIII. fig. 5). 



9. Diagram of circulation in the abdomen of Scorpio ; the left half represents a section posterior to 



that of the right half; h, the heart, on the right it is discharging blood through a short passage 

 (artery) among the digestive tubules below the visceral membrane (?«). Lb, lung-book, the 

 leaves of which are so arranged that blood both from the ventral sinus [vs) and from the 

 alimentary diverticula can flow out sideways between them. nc, nerve-cord with an 

 accompanying blood-vessel, which discharges its blood into the ventral sinus (? and among 



