1866, ] LZoclogy, Animal Physiology, §c. 129 
which terrestrial Mollusks obtain food under circumstances of ex- 
treme drought. Travelling in the south of the province of Oran, 
in Alveria, he had occasion to notice great numbers of them in the 
steppes of the desert, and proved that they derived the water neces- 
sary for their nourishment from certain of those succulent plants 
which grow spontaneously ia arid situations, such as Atriplex hali- 
mus. ‘This plant appears also to be the chief food of the Meah 
antelope, which, the Arabs say, lives several years without drinking. 
Another such plant is the Bou gerba, or bottle plant, upon which 
he has seen nearly every morning, while there was still some fresh- 
ness in the air, hundreds of snails agglutinated. These Mollusks 
can exist for a long time without food, and are furnished, moreover, 
with a solid operculum, while the white colour, which appears to be 
characteristic of all the Saharian animals, defends them to a certain 
extent from the heat of the sun. Their shell also is relatively thick, 
for they all live upon the calcareous or saline plateaux of the desert, 
where they find abundance of material for the formation of their 
testaczous envelope. 
Dr. Phipson, in ‘ Cosmos,’ states that lately, beg at Marburg, 
he observed, about 10 p.m., certain luminous insects flying in the 
air on the banks of the river. On securing one, he found it to be 
a male Lampyris splendidula, proving that the male Lampyri enjoy 
the faculty of emitting light, about which there was previously some 
doubt. But M. Schultze has described, more than a year ago, the 
structure of the luminous organs of these very same male insects, 
the tracheze of which he finds to be terminated in a small cell of 
stellate form, which rapidly acquire a black tinge under the action 
of osmric acid, the cells of the parenchyma remaining uncoloured. 
Dr. Walsh describes, in ‘Silliman’s Journal,’ some very curious 
effects produced upon insects apparently by the material of their 
food, from which he is led to believe that otherwise identical insects 
differ, as varieties or species, according to the species of plant they 
feed upon. This difference of food may have very various results: 
sometimes it is accompanied by no difference whatever either in the 
larva, pupa, or imago state; but it may coincide with a marked 
difference in the colour of the silk-producing secretions, or a ten- 
dency towards the obliteration of the normal dark markings in the 
imago; or marked, but not perfectly constant, colorational differ- 
ences in the larva, but none whatever in the imago; or by a marked 
and perfectly constant difference in the size of the imago; or by a 
marked difference in the chemical properties of the gall-producing 
secretions, the external character of the imago remaining identical ; 
or by a slight but constant change in the coloration of the abdo- 
men of the imago, and a very slight change in the chemical pro- 
perties of the gall-producing secretions; or by one marked and 
VoL. III. K 
