310 Dr. Pakis's Remarks on 



1 shall close this paper with a iew 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 has 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 lime, may be shown by the following curious circumstance. 



A hen, 



