16 THE ZOOLOGIST. 
therefore are areas favourable for the development of stridulating 
organs; for in the great majority of cases—the Cicada, by the 
way, being a notable exception—-stridulation in the articulated 
animals results from the friction of two mutually roughened 
adjacent chitinous areas. 
Strictly speaking, however, this is not the case with the 
stridulating organs that have been found in the Spiders now 
under discussion; for in all cases these organs consist of 
modified bristles. In the Oriental members of the family two 
such organs exist, namely, the one discovered by Wood-Mason, 
and another discovered by myself in several more genera.* In 
both cases the organ lies between the outer surface of the 
mandible and the inner surface of the maxilla—the basal seg- 
ment of the palp; and each consists of a set of vibratile bristles, 
which are set a-twanging by a series of spines. But whereas in 
Wood-Mason’s instrument the vibratile bristles or notes are 
placed on the maxilla, and the spines or scraper on the mandible, 
exactly the opposite obtains in the other instrument, the notes 
being on the mandible and the scraper on the maxilla. 
In some of the African T'heraphoside I have also had the 
good fortune to discover two stridulating organs, which are not 
only quite different from each other, but also quite different from 
those possessed by the genera inhabiting Tropical Asia. One 
of these organs occurs in the genus Harpactira, the common 
“Mygale” of Cape Colony. It occupies the same position as the 
analogous organs existing in the Oriental species, being situated 
between the mandible and the maxilla. A glance at Fig. 1 will 
show the construction of the organ. The outer surface of the 
mandible (A) is furnished with a large pad of feathery hairs (0d), 
and on the area between this pad and the oral fringe (c) are two 
sets of bristles, both of which, judging from their colour and 
structure, originally formed part of the oral fringe, and have been 
derived from it Those of the upper series are long, and have 
their free ends bent over and more or less interlacing with each 
other. Those of the lower series are less regularly arranged. In 
the species figured they are short and spiniform; but in some 
allied forms they are much less distinctly differentiated from the 
* For descriptions and figures of these instruments, see ‘ Natural 
Science,’ vi. pp. 44-50, 1895. 
