18G Scientific Intelligence. — Zoology, 



which represents pearls as originating in abortive ova. The fol- 

 lowing are the results of Dr Baer''s investigations : 1. In the fresh 

 water mussels of Germany, though true pearls are rare, yet in 

 most of the species which he has examined, he has occasionally 

 succeeded in discovering them. 2. He has never met with them 

 either in the ovaries, liver, kidney, or any of the internal organs. 

 3. The pearls were always situated either in or under the skin 

 of the back, where it is close to the shell. 4. In the same part 

 of the integuments, small coagulated isolated masses are often 

 observable, exhibiting, however, no traces of organization. He 

 conceives, that the pearls are the result of an ulterior formative 

 process taking place in these isolated amorphous masses, and, 

 although comparatively few of them eventually undergo this 

 transformation, cannot be fairly urged as any objection to the 

 truth of his hypothesis. He suggests, that those only may 

 ultimately become enveloped with a layer of calcareous mat- 

 ter, which are nearest to the external surface of the integu- 

 ments, the natural organization of which adapts it for such a 

 secretion. This view of their formation is still farther sup- 

 ported by the fact of pearls having been found by other na- 

 turalists, not merely in the above described situation, but also 

 in free or unattached portions of the integuments, or in mantle 

 flaps. The observations of Reaumur in the Memoirs of the Aca- 

 demy of Paris (1717), as well as those of L. D. Herman, who 

 spent many years in the investigation of this subject, tend to cor- 

 roborate the opinion of Dr Baer. Even the drawing given by 

 Home vouches for the correctness of the German physiologist, as 

 the pearls in it are evidently placed in the integuments, namely, in 

 that part of them which is opposite to the heart, and to which 

 the ovary never extends. It is probable that, in some instances, 

 the little soft masses already alluded to became coated exter- 

 nally with calcareous matter, thus accounting for the cavity ob- 

 servable in many pearls ; whilst in others, on the contrary, they 

 become infiltrated and saturated with the same material, and 

 thus form solid pearls. That pearls are merely morbid concretions 

 may, indeed, be considered as long^since satisfactorily made out ; 

 the peculiar merit of Professor Baer consists in directing atten- 

 tion to the soft coagulum which precedes their formation. The 



