354 
THE OCEAN WORLD. 
fera; being the same secretion which in the pearl lias assumed the 
globular form : in one state it is deposited as nacre on the walls of th 0 
bivalve, in the other as a pearl in the fleshy interior of the anim* 1 • 
This nacre is therefore at once a calcareous and horny matter, '"due 1 
the animal secretes, and which it attaches to the interior walls of t^ e 
Fig. 145. Meleagrina margarit.ifera (Linnaeus). 
Outside of the shell. inside of the shell- 
shell during the several periods of its development. Pearls are for®' ^ 
of the same substance, only in place of being deposited upon 
valves in beds, the material is condensed and agglomerated in s®* 
spheroids, which develop themselves either on the surface of 
Fig. 146. Meleagiitia margaritifera (Linmuns). 
valves or in the fleshy part of the mollusc. Between nacre 9,0 
pearls, therefore, there is only the difference of the form of deposi - 
Pig. 146 represents the pearl oyster with calcareous concretions 
various states of progress. 
