22 NATURAL SCIENCE. July, 



this myself. Indeed, only three days ago, while walking into 

 Salisbury from the Umfuli, I met one in the road which hissed at me 

 on my approach. I watched to see from what part the sound pro- 

 ceeded, and it appeared to me to be caused by the movement of the 

 mandibles alternately backwards and forwards. I did not catch the 

 specimen, since it belonged to the species of which examples have 

 already been sent to you — in fact, the only one that I have seen 

 round Salisbury. I have also heard the common small black 

 scorpion of Natal make a similar noise, and this is a generally well- 

 known fact there. I have never examined a dead scorpion to find 

 the stridulating organ, but from the action of the living creatures I 

 presume it is very similar to that of Solpuga. The sound of the latter 

 is, however, much harsher and more grating than that of the 

 scorpion, which is best described as hissing." 



An examination of the mandible of the species referred to — 

 Opisthophthalmus glabrifrons — not only showed very clearly the position 

 and structure of the sounding organ, but also furnished an explanation 

 of the difference in tone between the stridulation of Solpuga and of this 

 scorpion. In the former, as is well known, the harsh grating noise is 

 produced by the friction of a set of hard coarse ridges, situated on the 

 inner surface of the mandible of one side, against an exactly similar 

 set upon the corresponding surface of the mandible of the other 

 side. In position the organ of Opisthophthalmus resembles that of 

 Solpuga, being situated upon the inner surface of the basal segment of 

 the mandible, and a further resemblance lies in the fact that the part of 

 the instrument on the right mandible is structurally similar to that upon 

 the left. In this respect the instrument, as a whole, is quite different 

 from the analogous instruments found in the species of Scorpio and in 

 the stridulating spiders of the family Aviculariidae, where two distinct 

 structures, namely strikers and notes, are involved in the composition 

 of the instrument. 



A glance at the annexed figures will show that the organ in 

 question consists of a set of delicate membranous notes, projecting 

 upwards from near the middle of the inner surface of the basal 

 segment (Fig. 4, A). In different species they vary, both in number 

 and form, being sometimes racket-shaped, with a long stalk (Fig. 4, D), 

 and sometimes heart-shaped, with scarcely any stalk at all (Fig. 4, E). 

 The latter kind is found in O. granifrons, the former in O. carinatus and 

 0. nitidiceps, while notes of an intermediate type occur in O. glabrifrons 

 (Fig. 4, C). The number also varies in different species, and appa- 

 rently in different members of the same species. For example, a 

 specimen of 0. carinatus from Otjimbinque has as many as eight 

 (Fig. 4, B) on each mandible, while a second from the Umfuli River 

 in Mashunaland possesses but five. Again, six were noticed in a 

 specimen of 0. latimanus, four in O. pugnax and 0. capensis, three in 

 O. breviceps and O. glabrifrons. But the exact systematic value of this 

 new character has yet to be determined. Apart from the distinctive 



