September 2, 1889.] Supplement to the "Tropical Agriculturist." 
219 
form of carved work is represented. Thus it can be 
imagined how striking is the effect produced iu one of 
these limestone epveri a. where the whole structure seems 
to rest on beautiful columns of Nature's own architecture, 
which appear to have been intentionally designed fcr 
the purpose of support. Though I am told thaS 
stalactitic caverns exi't in the island, I can gather no 
definite information on the point, but the anpearanco 
of small stalactites may be observed under old road- 
bridges or culverts. 
Coral Formation. — Coral reefs flank many partR 
of the coa?t of Oeylon, and the/ barrier reef on the 
S.-W. coast is fa.miliar to most people who have 
travelled south by the sea side. Here we have o,n organi- 
cally-formed structure, the organic agent being the coral 
zoophyte, which has the power of appropriating the 
carbonate of lime in the sea for building ca'careous 
structures for themselves. These reef-builders require 
a temperature somewliat above 68° F. to flourish, 
and they do not thrive below 100 feet below sea- 
level. The extent of 1he coral-nuilders, work may be 
imagined, when it is said that the great barrier reef 
of East Australia varies in breadth from 10 to 90 mi'es 
and extends for a distance of 1,250 miles. A barrier 
reef is one that rises up in front of a steep shore, — 
the mainland or an island — between which and the 
reef is a body of water, while a fringing reef is 
one that extends from land seaward till the limit 
of depth at which the reef-builder flourishes is 
reached. An atoll again is a lagoon surrounded by a 
ring of coral. The theory of Darwin to account for 
these formations is as beautiful as it is ingenious. 
Darwin supposed that an atoll began by being a 
fringing reef, next a barrier reef, and lastly an atoll. 
The fringing reefs, he supposed, were formed round some 
island. His great hypothesis, however, was that 'here 
was a gradual subsidence of the sea-bottom which 
kept pace with the rise of the coral bed, as the 
result of the coral-builders' work. Thus the barrier 
reef would naturally follow, and after the subsidence 
of the entire island below the sea-level, a lagoon 
would take its place, the result being an atoll. 
This explanation, however, is now rejected by 
geologists as the result of further research in thia 
direction. Mr. Murray of the " OhalleDger " Expedition, 
supported by Professor Agassiz, has been instrumental 
in overturning the long-accepted theory of Darwin. 
Mr. Murray, in the course of his observations, dis- 
covered th't the islands round which, or upon which, 
the coral builders are at work, are of volcanic origin, 
and show no trace of subsidence. They are exclusively 
made up of volcanic material, and none which are 
below the sea-level, as the bases of an atoll, shows 
any of the unmistakable evidences of having been 
at one time above sea-'evel. This at once did away 
with Darwin's romatitic, though, it must be admitted, 
rather sweeping hypothesis, as to the mutual understand- 
ing between the coral builders and the Plutonic agencies 
of the earth. In contradistinction, Mr. Murray ac- 
counts for the lowering of the levi 1 of these volcanic 
islands by the more matter-of-fact and accept-) ble 
explanation, that it is owing to the disintegrating 
action of the waves, which thus brings the island 
within the sphere of the coral-builders' work ; while 
submarine islands may have had their level gradually 
raised to the required elevation by accumulations of 
organic remains. This, agreeing as it does with other 
well-known geological results, is a very plausible theory. 
Thus, reefs growing upward from submerged banks 
would form atolls ; while fringing reefs and barrier 
reefs would form round islands of higher levels. It is 
known by observation that certain areas on our globe 
do undergo, and are undergoing, a process of gradual 
subsidence as described by Darwin, and Mr. Murray 
grants that certain atolls may owe their existence to 
such a phenomenon, but an overwhelming amount 
of evidence militates agaii st any attempt at making 
Darwin's hypothesis account generally for the for- 
mation of friuging-reefs, barrier-reefs, and atolls. 
Old coralline formationu appear as the coral-rag 
of the Oolitio period, and the coralline crag of tbe 
Pliocene period. Thero are some splendid specimens 
of cora'line structures in the Colombo Museum 
LIFE-HISTORIES OF INSECTS INJURIOUS TO 
VEGETATION IN CEYLON. 
II. 
By Aba. 
Insect-eggs. — Insects pass through many changes o^ 
form attended by remarkable changes in their habits. 
These changes or metamorphoses as they or e technically 
called mii;ht cause the same insect, at different stages 
cf its life to be mistaken for so many different animals. 
The first stage in which the greater paH of insects 
appear is that of an ovum, some few however are 
produced alive, as some fly maggots and tbe .maimer 
broods of tbe aphides. Insec'-eggs vary much inform 
and color. They are either oblong, round, conical or 
oval, and are yellow, orange, blue, &c. 
Larva, commonly known as maggot, caterpillar and 
grub, is batched from the e,?g, excep' in the cases 
before mentioned. The larva differ materially according 
to the different tribes to which tbey be'ong. There 
are some insects, however, which undergo no change 
of shape, as the grasshoppers and crickets. These are 
hatched from the eggs complete iu all their parts, 
and undergo no further change than that of casting 
their skin from time to time and gradually increasing 
in size, till at length they acquire a perfect resemblance 
to the parent insect. Maggots are produced from tbe 
eggs of two-winged (dipterous) flies, bees or wasps. 
They are of a white or grey color and legless. The 
larva of molhs and butterflies are called caterpillars. 
They are very often beautifully marked and are fur- 
nished for the most part with a pair of articulated 
feet on each of the three segments behind the head, 
and pairs of fleshy appendages called sucker-feet on 
some of the other segments, and at the end of the 
tail (known as tbe caudal proleg). Grubs are hatched 
either from the eggs of weevils or beetles. The best 
known are these of the cockchafer which is so de- 
structive to vegetation. But whether in this shape or 
in the s hspe of a maggot or caterpillar or whatever 
kind of insect it may be at this stage of its life, it 
is scientifically known as a larva, a Latin term 
which means, a mask because in this stage the 
future form of the insect is masked or concealed. 
In the larval stage the insect feeds voraciously and 
often grows rapidly. With the growth of the insect 
the skin does not expand beyond a certain limit, and 
when this point is reached the larva ceases feeding 
for a time, during which the skin loosens, cracks and 
is cast off. This operation is called moulting and occurs 
from time to time till the larva reaches its full growth. 
At each moulting the larva comes out in a fresh coat, 
sometimes like the previous ore, but very often of a 
different color or differently marked. The duration of 
life in the larval stage varies from a wsek or two, 
to a period of three or four or even five years, as 
with the wireworm and dragon fly. 
Pupa. — When the larva attains its full growth it 
ceases to feed and seeks a shelter in which it may 
change from the state of larva to that of pupa. For 
instance, a caterpillar after feeding till it reaches its 
full growth retires into some place of concealment, 
casts off its caterpillar-skin and appears in an entirely 
different form. In this new form the insect seems 
for the most part to be a lifeless oval, oblong or 
conical body. In the different tribes of insects the 
pupa or chrysalis (the term is used in the case of 
moths and butterflies) differs as much as the larva. 
In the majority of the beetle tribe it is furnished 
with Hmb3 which are cased in sheaths and folded 
beneath the breast ond body. The pupa of the butter- 
fly on the other hand is quite destitute of limbs and 
merely exhibits a writhing motion when touched. It 
is very often adorned with golden spots or otherwise 
beautifully marked, henoe the name of chrysalis. The 
pupa of the locusts and grasshoppers differ only from 
the perfect insect in having the wings incomplete. In 
the fly tribe the pupa is perfectly oval, without any 
motion or distinction of pnrts. The pupa of the 
dragon-fly is very active and liveB in water, but differs 
very widely in appearance from the perfect insect. 
After resting a while in the pupal state, an inward 
