308 ZOOLOGY 
oesophagus leads from this sac to a second enlargement, which 
receives the ducts of a pair of salivary glands, structures 
which are usually associated with a terrestrial mode of life. 
The succeeding digestive portion of the alimentary canal re- 
mains narrow; it receives four or five ducts which convey the 
secretion from a corresponding number of lobes of the liver. 
The latter is a considerable gland which takes up a good deal 
of space in the wide mesosoma, and even extends into the 
narrow metasomatic segments. One or two pairs of delicate 
Malpighian tubes are present, and these have been recently 
shown in one species to be developementally outgrowths from 
the mesenteron ; a pair of these tubes are branched. A procto- 
daeum is present, and ends in an anus situated ventrally at 
the end of the metasoma. 
The heart in Scorpio, as in Limulus, consists of a median 
tube of eight chambers ; it is continued backward in the scorpion 
as a posterior aorta which traverses the metasoma. A pair of 
valvular ostia open into the anterior end of each chamber, 
and a pair of lateral arteries take their origin from the pos- 
terior end of each division, The eight chambers lie in the 
seventh to the thirteenth segments, the last containing two 
chambers. From the anterior end of the heart a truncus 
arteriosus leads forward; this vessel gives off two lateral 
branches, which embrace the oesophagus and then unite into a 
median artery which runs backward above the nerve cord. 
In front of this ring the anterior aorta divides into two lateral 
vessels and a median one, these supply the appendages of the 
prosoma, the brain, and other organs. After passing through 
the body, the blood collects in a ventral reservoir and passes 
thence to the lung-books. Here it is oxygenated, and is then 
conveyed by special veins back to the pericardium, and so 
into the heart. The blood in Androctonus is, when oxygenated, 
of a deep indigo blue, coloured by haemocyanin ; its corpuscles 
are oval, and are remarkably large. 
The four pairs of oval stigmata, which are obliquely placed 
on the sterna of the ninth, tenth, eleventh, and twelfth seg- 
ments, lead into sacs, into the lumen of which project numerous 
lamellae. These lamellae, of which there may be as many as 
130, arise from a definite axis, which is for the most part 
