xi ANATOMY 305 
glands, often called salivary glands. The succeeding portion in 
the prosoma receives four or five more pairs of ducts from the 
well-developed gastric glands. In the rapidly narrowing first 
metasomatic segment the intestine receives one or two pairs of 
Malpighian tubes, and thence proceeds to the anus, situated 
ventrally in the last segment. 
The vascular system is of the usual Arachnid type, the 
heart being a seven-chambered dorsal longitudinal vessel lying in 
a pericardium, with which it communicates by seven pairs of 
valvular ostia. Lankester’ has demonstrated several pairs of 
superficial lateral veins connecting two deep-seated ventral 
venous trunks with the pericardium. © The lung-books are, so to 
speak, pushed in to dilatations of these trunks, so that some of 
the lateral veins carry blood newly aerated by the lung-books 
directly to the pericardium. 
The nervous system is not greatly concentrated except in 
the prosoma, where there is a single ganglionic mass which 
innervates not only the whole prosoma but the mesosoma as far 
as the fizst and sometimes the second pair of lung-books. There 
are two mesosomatic ganglia, variously situated in different 
genera, and each metasomatic segment has its ganglion. 
The generative organs are more or less embedded in the 
gastric glands. There are two testes, each composed of a pair 
of intercommunicating tubules, and connected by a common vas 
deferens with the generative aperture, which is furnished with 
a double protrusible intromittent organ. <A pair of vesiculae 
seminales and a pair of accessory glands are also present. The 
female possesses a single ovary, consisting of a median and two 
lateral tubules, all connected by cross branches. 
In addition to the external sclerites a free internal skeletal 
plate, situated in the prosoma between the alimentary canal and 
the nerve-cord, furnishes convenient fulera for muscular attach- 
ment. It is known as the “ endosternite.” 
Brauer? has made the most complete study of the develop- 
ment of Scorpio, and two of the most interesting of his conclusions 
may be mentioned here. He has shown the lung-books to be 
derived from gills borne on mesosomatic appendages. Moreover 
he found in the embryo five pairs of segmental ducts—in 
1 Tr. Zool. Soc. xi. part x., 1885, p. 373. 
2 Zeitschr. wiss. Zool. lix., 1895, p. 351. 
WAODES. JIMS x 
