40 CHARLES DARWIN 



the water, and sends forth a pleasing chirp: when several 

 are together they sing in harmony on different notes. I had 

 some difficulty in catching a specimen of this frog. The 

 genus Hyla has its toes terminated by small suckers; and I 

 found this animal could crawl up a pane of glass, when 

 placed absolutely perpendicular. Various cicidae and crickets, 

 at the same time, keep up a ceaseless shrill cry, but which, 

 softened by the distance, is not unpleasant. Every evening 

 after dark this great concert commenced; and often have I 

 sat listening to it, until my attention has been drawn away 

 by some curious passing insect. 



At these times the fireflies are seen flitting about from 

 hedge to hedge. On a dark night the light can be seen at 

 about two hundred paces distant. It is remarkable that in 

 all the different kinds of glowworms, shining elaters, and 

 various marine animals (such as the Crustacea, medusae, 

 nereidae, a coralline of the genus Clytia, and Pyrosma), 

 which I have observed, the light has been of a well-marked 

 green colour. All the fireflies, which I caught here, belonged 

 to the Lampyridae (in which family the English glowworm 

 is included), and the greater number of specimens were of 

 Lampyris occidentalis.* I found that this insect emitted 

 the most brilliant flashes when irritated: in the intervals, 

 the abdominal rings were obscured. The flash was almost 

 co-instantaneous in the two rings, but it was just perceptible 

 first in the anterior one. The shining matter was fluid and 

 very adhesive : little spots, where the skin had been torn, con- 

 tinued bright with a slight scintillation, whilst the uninjured 

 parts were obscured. When the insect was decapitated the 

 rings remained uninterruptedly bright, but not so brilliant 

 as before: local irritation with a needle always increased 

 the vividness of the light. The rings in one instance retained 

 their luminous property nearly twenty-four hours after the 

 death of the insect. From these facts it would appear proba- 

 ble, that the animal has only the power of concealing or 

 extinguishing the light for short intervals, and that at other 

 times the display is involuntary. On the muddy and wet 

 gravel-walks I found the larvae of this lampyris in great num- 



4 I am greatly indebted to Mr. Waterhouse for his kindness in naming 

 for me this and many other insects, and in giving me much valuable 

 assistance. 



