310 Dr. Parıs’s Remarks on 
I shall close this paper with a few observations on the forma- 
tion of the exterior involucrum, or shell, by which this microcosm 
is defended from external violence. We here detect a single 
operation, at once answering two of the wisest and most import- 
ant purposes of the animal: it at once averts destruction from the 
individual; and contributes essentially to the preservation of its 
species; for, whilst it removes the calcareous matter, which, if 
allowed to accumulate, must render the bird incapable of flight, 
and defeat the best purposes of its existence, it furnishes the 
germ of the future animal with a strong and convenient defence. 
The eggs of birds are, however, sometimes destitute of this pro- 
vision, which I think may arise from the secretion of calcareous 
matter not keeping pace with the exuberant production of the 
fluids of the egg. Hence we perceive this imperfection oftener 
occurring in strong birds, and in the months of harvest, when 
their food is more luxuriant and abundant. The experiments 
of Vauquelin, which prove that the quantity of calcareous 
matter voided by birds exceeds that taken in, suggested to - 
Fordyce, that birds must require calcareous matter during their 
laying, and that, if the animal be deprived of it, the shell is never 
formed. Such a theory, however, is not only derogatory to the 
wisdom of nature, but illegally deduced from the experiments 
themselves. Are we to expect, from our imperfect notions of 
elementary bodies, to explain the origin of every substance found 
in the animal ceconomy, or the series of changes which it under- 
goes? Nature bas her own laboratory, and is capable, without any 
foreign aid, of preparing the ingredients necessary for her pro- 
ductions. That a deficiency of calcareous matter in the system 
is the cause of the absence of the shell, no one will deny; but 
that this depends on some internal state, and not on the privation 
of line, may be shown by the following curious circumstance. 
- A hen, 
