ANATOMY OF THE LAMELLIBRANCHIATA. 443 



or canal leading from the ovaria to the cavities of the bran- 

 chics. Cams, though incorrect in the opinions formerly pub- 

 lished by him on this subject, has, ^n another work, ascer- 

 tained the true anatomy and functions ; and the author can 

 vouch for his accuracy, as he has obtained nearly the same 

 results. 



DISEASES AND PARASITICAL ANIMALS, 



One of the most remarkable circumstances relating to these 

 animals is the generation of pearls: 1 the subject has been 

 treated of by Home and many other writers. These calcare- 

 ous concretions appear to be generally formed around abor- 

 tive ova, as was known to Pliny. The most beautiful ones 

 are obtained from the Meleagrina margaritifera, which in- 

 habits the Indian seas. The interior of this shell likewise 

 furnishes the nacre, or mother of pearl. Pearls of value are 

 likewise occasionally obtained from the Unto margaritifera, 

 a British species. Pearls are also common in other bivalves, 

 as in the Anodontce, Pholades &c, but are never of any beauty. 



Numerous parasites inhabit the bodies of the Lamellibran- 

 chiata. Baer 2 has described many of those of the fresh 

 water species, but has often considered vibratile parts of the 

 animal to be such. 3 His Aspidogaster conchicola is very 

 common in the pericardium, secreting organs, &c, of the 

 JJnio and Anodonta. The author found the ovaria of an 

 Anodonta enormously distended with parasitical ova, which, 

 ruptured, were each found to contain several young individu- 

 als of a species of Distoma. The Nnmmulella of Cams ap- 

 pears to be produced by the rolling upon itself of a branchial 

 particle. The Peripheres conchilis spermatica of the same 

 author, abounds in the branchice. Many other animalcules 

 are also found. In the ovaria of another Anodonta the author 

 found a parasite in the different stages of its growth. In the 

 mature state its body is more or less cylindrical in shape, but 

 varying much at the will of the animal ; at one extremity are 

 two long appendages, which are spiniferous at their termina- 

 tion, and, in some individuals have a row of round bodies at- 

 tached to one side, for part of their length ; these appendages 

 are contracted with great rapidity, and are then very short. 



1 Vogt, ' De Causa Margaritarum,' Nov. Act. Acad. Nat. Cur. vol. viii. 



2 Nov. Act. Acad. Nat. Cur. vol. xiii. The author has only seen the ex- 

 tracts from the papers of Baer in the Bull, des Sci. Nat. and in the Zoo- 

 logical Journal. 



3 Raspail, Isis, 1827, &c. See also Gaillon, ' Sur les Animalcules des 

 Huitres,' Mem. Acad. Rouen, 1820. 



