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CONSTRUCTION OF SHELLS. oO 
by the filaments of which this membranaceous 
substance is composed. In analysing shells of a 
finer texture than such as are generally submitted 
to the test of experiment, the greatest circumspec- 
tion is necessary. So much so, that M. Herissant, 
whose attention was particularly devoted to the 
subject, after placing a porcelain shell in spirits of 
wine, added from day to day, for the space of two 
months, a single drop of spirits of nitre, lest the air, 
generated or let loose by the action of the nitric acid 
on the earthy substance, should tear the net work of 
the fine membranaceous structure. This gradual 
operation was attended with complete success, and a 
delicate and beautifully reticulated film, resembling 
a spider’s web in texture, rewarded the patience of 
the operator; the organization of which, from its 
extreme fineness, he was not, however, able to de- 
lineate. In shells of peculiar delicacy, even five or 
six months are sometimes necessary for their com- 
plete development ; but, in others of a coarser texture, 
the process is soon completed. 
Many beautiful configurations and appearances are 
afforded by the membranaceous part of different shells; 
those especially which are disclosed in the lamine of 
the Oyster, River Muscle, and Sea-Ear, after exposure 
to the action of diluted nitric acid. 
These elegant marine productions are well known 
