that throughout these vast areas, wherever there is now 
an “ Atoll,” a foundation must have originally existed 
Family— MADREPORITID iE. 
within a depth of from twenty to thirty fathoms from 
In this family the animals live crowded together in 
the surface.” Taking this as a certainty, he solves all 
societies, forming a branched coral; and the cellular 
difficulty as to the origin of these immense structures. 
substance of the animal is in general not so perfectly 
by saying that wherever these “ Atolls” occur there 
filled with calcareous matter as in the preceding family. 
must have been a gradual subsidence of land, which 
In consequence of this, we find the species to be of a 
served as a basis for the polypiferous corals to erect 
more spongy or a lighter texture. It is, however, of 
their wonderful structures upon. The Polypes never 
these that the coral reefs are chiefly formed. Mr. Dar- 
build their corals above low-water mark; hence the 
win found on the edges or outer margins of the reefs 
coral islands and reefs never rise many feet above the 
of the Lagoon islands, that a species of the genus 
surface. The elevation of the land upon them is prin- 
Porites was the most abundant, and that it formed 
cipally owing to the action of the sea. Large masses 
great irregularly rounded masses from four to eight 
are detached by the waves and washed upon the reef ; 
feet broad, and about the same in thickness. The 
shells, coral, and other debris are likewise washed up 
fringing reefs, again, of the Mauritius had their outer 
on to it, and accumulate till a surface is formed with a 
edges formed of great shapeless masses of branching 
layer of soil upon it capable of supporting various forms 
Madrepores, belonging chiefly to two species, the Mad- 
of vegetable life. 
repora corymbosa and M. poeillifera. 
There are numerous genera and species of coral, the 
variations of form depending upon the manner in which 
Family — MILLEPORID.®. 
the animal emits from the whole surface, or from a 
According to Mr. Nelson, the animals forming the 
particular part of the sides of its body, the bud by 
corals belonging to this family are very different 
which the new individuals of the general mass or society 
from those of any other coral, being quadrangular. 
are produced. The specimens usually shown in col- 
expanded at intervals into four rays, and destitute 
lections are small individuals which grow in sheltered 
of any true tentacles. — ( Gray.) The greater bulk of the 
places among the rocks, where they are not exposed 
described species of millepores are fossil. A few, how- • 
to ihe action of the waves, and collected before they 
ever, are recent ; and one of these {Millepora compla- 
have reached their proper magnitude. The illustra- 
nata) is said by Mr. Darwin to be next to Porites in 
tions in Plate 2 of the various genera of corals, give 
abundance, as forming the reefs of the Lagoon islands. 
a very poor idea of the beauty of these formations. 
This species appears to possess the stinging or nettling 
In the family Madrephylliidse the genus CaryophylUa 
power possessed by the Actiniae. Lieut. Burnaby, 
is represented on Plate 2, figs. 6-7, by the CaryophylUa 
R.N., informed the writer of this, that at the Cocos or 
solitaria. The genus Astrsea is represented at figs. 
Keeling islands he had often experienced this fact. 
4-5, hy Astreea ananas; the genus Meandrina, or Brain 
Mr. Darwin, at the same locality, says that he found 
Coral, at figs. 10-11 by Meandrina lirnosa; and at fig. 3 
both this species and Millepora alcicornis to possess 
by M. cerebriformis ; and the genus Oculina is repre- 
this power. The family is represented in Plate 1, 
sen ted at figs. 8—9 by Oculina varicosa. 
fig. iO, by the species Millepora spongites. 
Sub-class II. — POLYZOA or BRYOZOA (Molluscan Zoophytes). 
By many naturalists this sub-class of Zoophytes is 
class Polyzoa have been arranged in two orders, accord- 
placed in the sub-kingdom Mollusca. In some respects. 
ing to the disposition of the tentacles which surround 
as we have observed already at the conclusion of our 
the mouth — 1st, Those which have the tentacles dis- 
article Mollusca, the species are closely allied to 
posed in a ring surrounding the unarmed mouth — all 
those of the class Tunicata, more especially the family 
Botryllida. or Compound Ascidians ; and in others they 
approach the Terehratulce amongst the Brachiopoda. 
The Polyzoa are compound animals, and the growth 
formed by the associated animals or colony, is termed 
“ polyzoary,” corresponding with the “ polypidom” of 
natives of the sea, the Infundibulata ; and 2nd, Those 
in which the tentacles are disposed in a crescent, or 
horse-shoe shape — all natives of fresh water, the Hippo- 
crepia. 
Order L— INFUNDIBULATA. 
the Anthozoa. This is formed of a number of little 
This order is by far the most extensive in number. 
chambers, or cells, organically united, each of which 
The animals have the tentacles disposed in an unin- 
contains a polypide. They possess organs of digestion. 
terrupted series round the annular disc surrounding the 
respiration, and circulation, have a muscular and 
unarmed mouth. This order is represented in Plate 1, 
nervous system, and in an embryonic state are fur- 
fig. 8, by Bicellaria fastigiata ; in fig. 7, by Cellepora 
nished with organs of motion. Their reproduction is 
effected in three different modes ; by gemmation, by 
hyalina; and in fig 11, by Serialaria lendigera. 
ova, and by what have been called free locomotive 
embryos. 
Order IL— HIPPOCREPIA. 
The numerous species of animals belonging to the 
This order contains only, comparatively speaking, 
