230 Mr. R. I. Pocock on a new Sound-producing 
which no person, one would have thought, could mistake for any- 
thing but immature. No doubt this is partly to be explained 
by the unfortunate circumstance that in the case of the females 
of this group of spiders—this being the sex which most fre- 
quently comes to hand—it is very hard to tell the adults from 
the immature. Consequently the generic status of every 
species, referred to sections a, a, or 0 of the above table, that 
rests solely upon a female specimen, must be regarded as of 
questionable validity, unless the maturity of the type specimen 
is beyond dispute. With the males the case is different. As 
a rule generic characters in this sex are pretty obvious ; and 
it may safely be stated that, until we know the males of the 
different species of Neotropical Theraphoside, the classifica- 
tion of this family will remain more or less chaotic. 
So far, however, as I can judge from the material at my 
disposal, the Homeommatee, Kurypelmatee, Theraphosez, 
Avicularier, Crypsidromez, Cheetopelmatez, and Ischnocolez 
form a compact and natural assemblage which may be called 
Theraphoside sensu stricto. But touching the [schnocolez, 
I must speak with some caution, since the genus Jschnocolus, 
from the Mediterranean, is unknown to me. 
XXXIII.—On a new Sound-producing Organ in a Spider. 
By R. I. Pocock, of the British Museum of Natural 
History. 
In January of the current year I published in ‘ Natural 
Science’ a brief summary of the present state of our know- 
ledge of the structure, position, mechanism, and function of 
the various kinds of stridulating-organs that occur in spiders, 
and I suggested that the available evidence seems to point to 
the conclusion that these organs have been evolved within 
the group in response to two needs, which, although totally 
different in their nature, are, in their way, alike of vital 
importance to the welfare of the species. In one set of 
species the sound is attractive and in the other repellent, the 
sense of attraction lying between members of opposite sexes 
of the same species and that of repulsion being experienced by 
enemies that might otherwise with intent or by accident destroy 
the spider if not warned of its presence and formidable nature. 
In connexion with the stridulating-organs that belong to the 
first category and are of sexual significance, it was pointed 
out that they are either absent or imperfectly developed in 
the females, and are perfected only in the males; whereas 
