COMPARATIVE MORPHOLOGY OF THE GALEODIDiE. 415 



Fig. 18. Left side of the alimcutary canal dissected from the cephalothora.x of Galeodes arabs. \, 2, 3, 4, 

 the four pairs of divcrticuh* ; ad, a small accessory diverticulum ; h, heart ; e, upper edge 

 of endosteruite ; T>, diapliragm. 

 19. Optical section of one of the above mid-gut diverticula, cleared in cedar-oil. Itn, longitudinal ; 

 an, circular muscles. 



Plate XXXIII. 



Fig. 1. Diagram of the alimentary system in the abdomen, to show the position of the dorso-ventral 

 muscles cut through. The diverticula filling the whole abdomen [cf. fig. 5) have only one 

 pair of apertures (ap) into the central canal {mg), viz., in the first segment. They, the 

 diverticula {div), open along the rest of the abdomen into two lateral canals [Ic] ; mat, 

 Malpighian tubules ; stp, stercoral pocket. 



2. A transverse section (camera lucida), taking in a portion of the diaphragm (D), cut tangcntially, 



showing the small size of the aperture for the alimentary canal {in); b, the heart; 

 //•, trachea. 



3. Slightly further back (drawn to the same scale), letters as in last figure. dim, dorsal longi- 



tudinal mu.scles ; w, neural aperture. 



4. Still further back, showing the pair of apertures {ap) of the diverticula into the central canal, 



drawn to the same scale ; letters as before. Only a very few of the crowded diverticula 

 are drawn, and some are drawn empty. n, the neural sinus, continuing the neural arch of 

 the diaphragm conveying the blood from the cephalotliorax into the abdomen ; the nerve- 

 strands are in its base, y, genital atrium, the chitinous lining has left the epithelium ; 

 ^^, accessory glands, opening one on each side of the genital aperture, and belonging morpho- 

 logically to the opercula {cf. yg, PI. XXIX. figs. II, 13) ; cf, chitinous thickening shown in 

 Plate XXIX. fig. 7, as continuations of the inter-articular fold between coxa and trochanter 

 of the preceding limhs ; /, faeces. 



5. Section of a distended abdomen (camera lucida), the diverticula drawn empty, g, genital glands ; 



tr, main trachea {cf. PI. XXX. figs. 13 and 14) ; do, fragment of a dorso-ventral muscle; 

 vim, ventral longitudinal muscle-band; lin, lateral muscles; /, faical masses in the mid-gut. 



6. Section through the waist of a Spider, to show the possibility of constricting the alimentary 



canal {in) by means of dorso-ventral muscles, h, heart (artery) ; n, nerve. 



7. Transverse section through the posterior end of mid-gut {mg), where the lateral canals (/c) 



are closely applied to it on each side (see diagram, fig. I). The mid-gut is surrounded by 

 circular and longitudinal muscles, outside which are tracheal tubes embedded in a spongy 

 layer of coagnlum, fluid-passages and ? cells {cf. sp, figs. 8, 9, 11). This spongy mass 

 surrounding the mid-gut is embraced by the lateral canals (/c), which are joined together 

 above and below the mid-gut by transverse muscles {tni}. The epithelium {mep) of the lateral 

 canals where they are in contact with the mid-gut is modified as described (text, p. 360). 

 The rest of the epithelium is so crowded with food-globules, that the individual cells are 

 no longer distinguishable. /, fsecal masses ; mal, Malpighian tubules ; tr, tracheae ; n, nerves ; 

 div, digestive diverticula witli epithelium disorganized by food-globules. 



8. Longitudinal section through the junction of the mid-gut and hind-gut of a distended Galeodes. 



mg, mid-gut; /ig, hind-gut; .^tp, stercoral pocket; tm, muscles binding the lateral canals on 

 each side of the mid-gut {cf. fig. 7) ; sp, spongy layer surrounding the posterior end of the 

 mid-gut. The crowded contents of the mid-gut, hind-gut, and stercoral pocket omitted. 

 The complicated folding of the chitinous wall of the stercoral [locket is suggested. The 

 thread-cells (fig. II) outside the commencement of the hind-gut gradually change to a tesselated 

 epithelium covering the end of the hind-gut and the stercoral pocket. 



