90 
VENUS’S FLOWER-BASKET.” 
[Nature and Art, March 1, 1867. 
of this description, are of a very large size, and 
unceremoniously seize on any tenantless shell of 
convenient form they can discover, seeking a new 
habitation as their growth increases, and leaving 
the old one for another tenant of less ambitious 
requirements. Crabs with habits such as these 
would not fail to investigate a hollow tube of such 
a tempting appearance as the young, growing, and 
coverless Euplectella would present ; and what 
more probable than that, as the tube became 
perfected and the lid partly made, the crab or 
crabs might still continue to inhabit it, until the 
orifice being at last closed up, Cancer had to remain 
a captive. His cast-off shells, like old worn-out 
garments, would remain sealed up with him, and 
give the idea that many crabs, instead of one, had 
there resided. 
Crabs do strange things at times, it is true, as 
we shall probably state in a future communication. 
But a Venus’s Flower-basket, we opine, is a work 
of too high an order for crustacean constructive- 
ness to grapple with. Sponges, on the other hand, 
we know to be workers in flint of the very highest 
order ; forming perfect tubes as their spicules, 
the external covering, like that of the wheat-straw 
or bamboo cane, being of pure silica, and the 
lining of a material allied to, if not actually, 
Tceratode, noticed by Dr. Bowerbank, and by him 
spoken of as “ one of the most elastic and durable 
animal substances.” No combination of material 
could be more pei’fect and comparatively inde- 
structible than this, combining, as it does, extreme 
flexibility with an almost indestructible surface. 
The silicious material of which these crystal- 
like tubes are composed is deposited in a series of 
concentric layers round a central tubular cavity, 
which gradually grows less as the spicules arrive at 
mature growth (vide fig. 9, plate 2, which repre- 
sents the adult or full-grown specimen of Spongilla 
Jluviatilis under the microscope, after having 
been subjected to heat, in order to char the con- 
tents of the interior, and so make them’ more 
evident). 
Fig. 10 shows a portion of a young and immature 
specimen from S. lacustrinus, treated in the same 
manner in order to show the greater size of the 
internal cavity and membrane lining it. The 
researches of Dr. Bowerbank, to whom we are 
indebted for our microscopic views, go to show 
that the silica is secreted by a double membrane, 
the inner surfaces of each alike possessing secretive 
powers. It will be seen that the Euplectellas are 
not the only sponges by many which secrete this 
curious flinty material, at times elaborated in the 
most beautiful and curious form. Fig. 1 is from 
E. aspergillum (Owen) • fig. 2 from a species of 
Euplectella deposited in the museum of the Jardin 
des Plantes , Paris. Fig. 3 is also from E. asper- 
gillum : whilst the curiously-hooked double grapnel 
or anchor form of spicule found in fig. 4 is from 
an undescribed sponge found on the coast of 
Sicily. Fig. 5 is from Halichondria incrustans ; 
fig. 6 from a spongeous mass found about the 
base or roots of E. Cucumer (Owen); fig. 7, from 
Tetliia ingalli (Bowerbank) ; fig. 8, from T. robusta, 
an Australian sponge. 
The form of some of these, especially that of 
fig. 3 and the two latter, ai - e such as to make us 
devoutly thankful that these highly useful creatures 
the sponges confine the manufacture of their spicules 
to microscopic minuteness, or using them for toilet 
purposes would be anything but an agreeable oper- 
ation ; but flint is not the only material of which 
a number of very curiously formed spicules are 
formed ; some sponges are most abundantly fur- 
nished with them, but composed of carbonate of 
lime.. It has been, however, observed, that al- 
though certain sponges have their surfaces covered 
with the carbonate of lime material and their in- 
teriors literally crammed with silicious spicules, 
j they do not naturally accompany each other, and 
are not secreted in common. The forms of the 
| sponges of commerce are too well known to need 
description, and although the life of a sponge may 
be a matter prosaic in the extreme and utterly 
devoid of the sensational element, there is much in 
it to interest the thoughtful observer of nature. 
Sponges are generated by what are called gemmules 
or minute atoms of gelatinous substance formed in 
the interior of the parent. These, as the flowing 
tide is absorbed and again expelled by the count- 
less orifices or oscula which cover the surface, are 
[ borne away with it, in association with the thou- 
sands of minute atoms from which the nutritious 
particles or organisms have been strained by the 
perfectly-formed structure through which they 
hare passed. These tiny sponge-seed are in some 
species covered with minute cilia or hair-like 
down ; others come forth mere gelatinous atoms, 
but possessed of rapid locomotive powers, moving 
here and there with surprising agility and 
speed. These after a short time become attached 
to a favourable object ; their secretive members 
are formed, and they remain, unless disturbed, in 
the position in which they first established them- 
selves. 
There are two theories to account for the absorp- 
tion and expulsion of water by the sponges. That 
of Dr. Grant favours the belief that the vast 
numbers of moving and vibratory cilia lining all the 
canals and cavities and bending their tiny arms 
like waving corn, thus set up a disposition in the 
water to flow ever onward through them. Dutrochet, 
however, attributes it to the law of endosmose , a 
very familiar example of which may be found by 
filling a common bladder with carbonic acid gas, 
when, after a short time, the gas, although of much 
greater weight than atmospheric air, will pass 
through the pores of the bladder and admit air. 
We leave the reader the option of selection between 
these theories, contenting ourselves by repeating 
that the sponge is fed and nourished by that which 
the flowing tide brings within the reach of its 
influence. Unlike the Actinia and some other 
stationary inhabitants of the deep, it has no arms 
or tentacles with which to reach forth and secure 
its prey ; therefore it makes of itself a living filter. 
The sponges, as a rule, are marine productions, 
