20 
Poisonous Arthropods 
THE SC 0 RPI 0 NIDA, OR TRUE SCORPIONS 
The true scorpions are widely distributed throughout warm coun¬ 
tries and everywhere bear an evil reputation. According to Comstock 
(1912), about a score of species occur in the Southern United States. 
These are comparatively small forms but in the tropics members of 
this group may reach a length of seven or eight inches. They are 
pre-eminently predaceous forms, which lie hidden during the day and 
seek their prey by night. 
The scorpions (fig. 11) possess large pedipalpi, terminated by 
strongly developed claws, or chelae. They may be distinguished from 
all other Arachnids by the fact that the dis¬ 
tinctly segmented abdomen is divided into a 
broad basal region of seven segments and a 
terminal, slender, tail-like division of five 
distinct segments. 
The last segment of the abdomen, or 
telson, terminates in a ventrally-directed, 
sharp spine, and contains a pair of highly 
developed poison glands. These glands open 
by two small pores near the tip of the spine. 
Most of the species when running carry the 
tip of the abdomen bent upward over the 
back, and the prey, caught and held by the 
pedipalpi, is stung by inserting the spine of 
the telson and allowing it to remain for a 
time in the wound. 
The glands themselves have been studied 
in Prionurus citrinus by Wilson (1904). 
He found that each gland is covered by a sheet of muscle on its 
mesal and dorsal aspects, which may be described as the compressor 
muscle. The muscle of each side is inserted by its edge along the 
ventral inner surface of the chitinous wall of the telson, close to the 
middle line, and by a broader insertion laterally. A layer of fine 
connective tissue completely envelops each gland and forms the 
basis upon which the secreting cells rest. The secreting epithelium 
is columnar; and apparently of three different types of cells. 
1. The most numerous have the appearance of mucous cells, 
resembling the goblet cells of columnar mucous membranes. The 
nucleus, surrounded by a small quantity of protoplasm staining with 
hematoxylin, lies close to the base of the cell. 
A true scorpion. 
Comstock. 
After 
