274 
DESCRIPTION OF A SPECIES OF GALL GNAT. 
principally flavescent olive, the dark san- 
guine hue (imperial purple of the ancients) 
being restricted to a band between the 
shoulders and bottom of the dorsal neck. So 
far from being “ exceedingly rare,” this 
species is much the most common of all, 
and I have now twenty specimens lying 
before me, notwithstanding my large des- 
patches to England. 
DESCRIPTION OF A DIPTEROUS 
FLY, THE LARVA OF WHICH PRO- 
DUCES A KIND OF GALL ON THE 
LEAVES OF THE FICIJS RACEMOSA. 
By P. F. H.Baddeley, Esq. 
For the India Review. 
A species of gall gnat (order, diptera ; 
tribe, cecydomyia) also deposits its eggs 
in the parenchymous substance of the 
leaf of the ficus racemosa, which turns into 
a small light coloured grub ; this latter, feed- 
ing upon the juices of the plant, changes 
into a chrysalis ; and this again, after a few 
days, into a little two winged insect. The 
larva, by its irritation, causes that part of 
the leaf in which it resides to swell into a 
flat kind of blister, in the centre of which a 
single insect is confined. 
The chrysalis is of a reddish brown co- 
lour approaching to black at the anterior 
part, where it is provided with four tuber- 
ches, having much the appearance of a pig’s 
snout : by means of these, it forces itself 
partly out from the under surface of the leaf, 
when, the skin bursting, the fly escapes. 
The^colour of the perfect insect is of a 
light brown with the antennae darker, and 
the head, which is entirely occupied by two 
compound eyes, black. Its body and wings 
are covered with long hairs. 
Metamorphosis . — Incomplete or coarc- 
tate. 
Wings. — Two, with large poisers. 
Antennoe. — Verticillate, composed of 24 
joints alternately large and small. 
EXPLANATION OF FIGURES. 
Figs. 1 and 2. — Under and upper surfaces 
of a leaf of the ficus racemosa containing 
several of these false galls. 
Fig. 3 — A section of one. 
Fig. 4 and 5. — Larva. 
Fig. 4 a. — Do. in the nucleus of the gall. 
Fig. 6. — Pupa. 
Fig. 7. — Perfect insect. 
Fig. 7. a . — Part of an antenna 
Fig. 7. b . — A wing. 
Fig. 7. c . — A wing magnified. 
GENERAL SCIENCE. 
NOTICE OF SOME RECENT IMPROVE- 
MENTS IN SCIENCE. 
HEAT AND LIGHT. 
1. TEMPERATURE OF THE GLOBE. 
— M. Poisson, in his elaborate work entitled 
Mathematical Theory of Heat, has broached 
some new notions in respect to the source of 
the earth’s heat. He observes, that the 
spherical form of the earth, and its flattening 
at the poles, prove that it was originally in a 
fluid, or perhaps in a gaseous state. After 
this period, it can only have become solid, 
either wholly or in part, by a loss of heat, 
proceeding from the circumstance that its 
temperature exceeded that of the medium in 
which it was placed. He conceives, that it 
has not been demonstrated that the solidifi- 
cation commenced at the surface, and gradu- 
ally extended to the centre, as those theorists 
assert who adopt the idea of a fluid centre. 
The contrary appears to Poisson more pro- 
bable; those portions nearest the surface 
having been cooled first, have descended into 
the interior, and been re-placed by matter 
from the interior, which has again descended 
in its turn, and thus the process was repeat- 
ed until the whole mass was cooled down. 
But further, the central layers would become 
solid, in consequence of the immense super- 
incumbent pressure at a temperature equal 
to, or even superior to that of the layers 
nearer the surface. Experiment has proved 
that water at common temperatures, when 
submitted to a pressure of lOOO atmospheres, 
undergoes a condensation of about i^of its 
original volume. Now, if we conceive a 
column of water equal in height to the earth’s 
radius, and reduce its weight to one half of 
what it possesses at the surface, in order to 
render it equal to the mean gravity of each 
radius of the earth, supposing the latter homo- 
geneous ; the inferior layers of this liquid 
column will undergo a pressure of above three 
millions of atmospheres, or equal to above 
three millions of times that which reduced 
the water of its volume. Without any 
knowledge of the laws of the compression 
of this liquid, we must still believe, that 
such an enormous pressure would reduce 
the inferior layers of the mass of water to 
the solid state, even when the temperature 
was very high. 
In order to explain the elevation of tem- 
perature which we observe, in proceeding 
from the surface towards the centre of the 
earth, he suggests the effect of the inequality 
