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. 



Fig. 227.— View of internal anatomy of Buthus, showing digestive, circulatory, 

 respiratory, and nervous systems. From Leuokart, after Newport and Blanchard. 



1. Chelicerae. 



2. Pedipalpi. 



3-6. Ambulatory limbs. 



7. Pectines. 



8. Mesenteron. 



9. Lobules of liver, with ducts 



entering mesenteron. 



10. Malpighian tubules, portions of. 



11. Procto4aBum. 



12. Anus. 

 13'-13'\ Lung sacs. 



14. Heart. 



15. Posterior aorta. 



16. Anterior aorta. 



17. Brain. 



18. Median eyes. 



19. Lateral eyes. 



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 



