IN GENERAL. 689 
reason why the formation of pearls should not be ascribed also to 
other irritants affecting the mantle. It has been observed at least 
that injuries of the shells and wounds, caused by boring worms, 
have had the production of pearls for a consequence; and the secret 
of Linn. aus for favouring the production of pearls (in Unio), con- 
sisted, most probably, in boring the shell in different places in con- 
chifers, which were submitted to these experiments}. 
The shells of molluscs, from their variety of colour and form, 
constitute no small part of the ornament of natural-history collec- 
tions. The knowledge of conchology is of the highest interest to 
the Geologist, since the petrified and extinct species afford im- 
portant characters for distinguishing the different strata. But, 
more than this, the knowledge of the molluscs is of great value to 
general physiology. To the celebrated Danish zoologist of the last 
century, O. F. MvELLER, the honour is principally due of having 
raised this part of natural history from the fondness of collectors to 
the scientific contemplation of naturalists; it was his impressive 
exhortation that thenceforward attention should not be confined 
solely to the house or the shell, but, above all, be extended 
to an accurate investigation of its inhabitant?. Already had Swam- 
MERDAM in Holland, and Martin Lister in England, investi- 
gated the internaf structure of some molluscs. Pott and Cuvier 
made this subject a primary object of their numerous inquiries, and 
thus, in the course of the last fifty years, and even in our own day, 
through the labours of De~tLe CHiAse, OWEN and others, a clear 
and extensive view has been obtained of a field of comparative 
anatomy that previously was almost unknown. This was an inesti- 
mable gain for a science which, if it is indeed to exercise an 
important influence on physiology, must not, in any sense, be 
limited to a few classes of animals, but must, in reality, be com- 
paring, and must compare generally. 
1 Compare Cuemnitz Vom Ursprunge der Perlen, Naturforscher, xxv. Halle, 1791, 
§. 122—130, and BecKMANN’s Geschichte der Erfindungen, cited there. On the origin 
of pearls from eggs of Conchifers see Phil. Trans. 1674, Vol. IX. pp. 11, 12, and 
especially E. Home in Phil. Transact. for the Year 1826, Part 3, pp. 338—341. This 
peculiarity had already been observed in 1673 by a Dane, H. ARNoLDI, at Christiana 
in Norway. 
2 See his Vermium terrestrium et flurviatilium Historia, Haunie, 1774, 4to. Tom. 1. 
Preefat. p. [. 
VOL. I. Af 
