Conchology. 235 



This, examined attentively, seems to be nothing else but a knot 

 of threads lying as close as possible to each other; this fibrous 

 matter discovers no sign of life, but, upon applying water to it, 

 the supposed fibres separate, and prove to be living creatures, by 

 motion at first languid, but gradually more vigorous. 



The Globe Animal. Fig. 15 represents this very singular 

 water animal, as it is seen before the microscope; its form seems 

 exactly globular, having no appearance of head or tail; it moves 

 in all directions, sometimes slow, and at other times very swift, 

 then swimming like a top; the surface of the body seems dotted 

 all over with little points, and beset round with hairs, which are 

 no doubt their means of motion. 



CONCHOLOGY. 



NO. VI. 



Of the Production of Pearls. In treating of the constitu- 

 ent parts of shells, it was observed that the composition of the 

 pearls, appears, from analysis, to be precisely the same as the 

 mother-of-pearl, or those shells in which the pearl is usually found. 

 From this we must conclude, that the pearl, and the mother-of- 

 pearl, are produced by the same secretion. It appears, from the 

 observations of naturalists, and indeed it might have been expected, 

 from the similarity of composition, that all testaceous animals, 

 whose shells come under the description of mother-of-pearl, occa- 

 sionally produce pearls. 



Different opinions have been entertained with regard to the 

 cause of the formation of this precious production. According to 

 some, it is merely a morbid concretion, formed within some part 

 of the body of the animal, or at least within the shell, without any 

 apparent external injury; while others suppose that it is only ow- 

 ing to wounds which the shell, or the animal, or both, have re- 

 ceived from accidental causes, or from the action of insects or 

 some testaceous animal, making perforations in the shell. It is 

 not improbable that pearls may be formed in both ways. 



Every day's experience informs us, that similar concretions are 

 formed in different cavities of the bodies of other animals, but 

 without any obvious cause, or external injury. The formation 

 of such concretions, as, for instance, biliary and urinary, calculi, 

 producing the most excruciating disorders in the human body, are 



