TRACHEATA 399 
adherent to the wall of the sac, only a short portion being free. 
Between the thin walls which constitute each lamella, the blood 
flows, whilst the air circulates between the lamellae. 
Z ENG fp E . | Less 
(On USES & re BPI : 
= 
19 : 
i 9 13" 8 ae caer 6 7 5 
Fic. 227.— View of internal anatomy of Buthus, showing digestive, circulatory, 
respiratory, and nervous systems. From Leuckart, after Newport and Blanchard. 
1. Chelicerae. 12. Anus. 
2. Pedipalpi. 131-13'%, Lung sacs. 
3-6. Ambulatory limbs. 14. Heart. 
7. Pectines. 15. Posterior aorta. 
8. Mesenteron. 16. Anterior aorta. 
9. Lobules of liver, with ducts 17. Brain. 
entering mesenteron. 18. Median eyes. 
10. Malpighian tubules, portions of. 19. Lateral eyes. 
11. Proctodaeum. 20. Poison gland. 
A pair of coxal glands occupy a position in the prosoma 
near the base of the fifth and sixth appendages; they appear 
to be actively secretory, but apparently in the adult have no 
outlet. In the embryo, however, according to Laurie, this 
gland originates as a tube which opens to the exterior at the 
base of the fifth appendages, and internally into a coelomic 
space. The coxal gland of Scorpio, like that of Limulus, thus 
seems to be of the nature of a nephridium, but the part 
which it plays in the excretion of nitrogenous waste matter, 
and whether it shares this function with the Malpighian 
tubules, is a subject still requiring investigation. 
The nervous system of Scorpio comprises a supra-oesopha- 
geal ganglion which sends nerves to the central and marginal 
