348 Hydra, or Fresh-water Polypus. 
to some increase of its thickness; not, however, by the addi- 
tion of any new layers, but by the eran of vitreous matter. 
Hence holes and canals, previously visible, are now filled up ; 
the aperture contracted, and the margins strengthened and 
enlarged; the upper part of the spire, perhaps, filled and 
marie cold: and the peculiarities which distinguish the sexes 
of the dicecious species fully developed. Foreign agents now 
begin to act, and the external layers lose their hair- “like coat- 
ing or their epidermis ; the colours become paler, and ulti- 
mately disappear ; striae and tubercles are smoothed and worn 
down; and parasites deform and perforate the outer surface. 
Death at length overtakes the architect, and the shell decays 
under the influences of the water and of the air. 
Such, then, is the manner in which shells are formed, so 
beautifully painted, and so curiously fashioned. ‘They are the 
house and str ong hold of their proprietors, to whose exist- 
ence, amid the str ae of elements, and the wiles and voracity 
of their foes, they seem essentially necessary. ‘The shells of 
the marine tribes, as was fit, are in general of great strength 
and hardness; or, if defective in these qualities, their weak- 
ness, through ‘le appliance of other means, is made strength. 
The river kinds are less har d, and thinner, being less exposed 
to the danger of a stormy element and a rocky Botton: ; while 
the shells of land snails are both light and thin, yet com- 
pletely impervious either to moisture or air. There is much 
to admire in all this: in the fitness of the shell to its element, 
in the art display ed in the building, and in the painting of the 
edifice, there is much to admire; and yet the possessor crawls 
on, unconscious of all, admirimg nought. Wherefore, then, 
this profusion of beauty? Surely the Creator hath pleasure 
in his works; surely Epictetus speaks the language of reason 
when he says, ** God hath introduced man tes the world to 
be the spectator of his works, and of their divine Author ; and 
not to be the spectator only, but to be the announcer and 
interpreter of the wonders which he sees and adores.” 
Iam, Sir, &c. G. Je 
Art. IX. On the Hydra, or Fresh-water Polypus. By SAMUEL 
Woopwarp, Esq. 
Sir, 
I am not aware that the subject of the Hydra, or fresh- 
water polypus, has been particularly noticed since the elabo- 
rate treatise published by Henry Baker, Esq. F.R.S., in 1743 5 
and, that work having become scarce, a few remarks may be 
interesting to your readers. 
