GENESIS OF PEARLS
	luster in white pearls and for the fact that the outer skins of very lustrous pearls are usually very thin also. Similar conditions exist in colored pearls, though the presence of a pig­ment makes them less noticeable. The skins of the haliotis pearl, which separate easily, usually show remarkable luster on the inner surface. Sometimes the nucleus is surrounded by a confused mass without apparent concentric markings, as though it had been enveloped in nacre which had solidified while stationary, or the first deposit shows the concentric skin arrangement at one segment of the circle only; followed by layers which appear in the depres­sions of the mass and are continued until they finally include the whole pearl. These layers are usually very thin, and the partial or seg­mentary layer formation is quite common in the early stages of the pearl's growth. At that period the concentric lines are also irregular, and in many cases where the curve is true, they extend about one quarter of the circumference only, another concentric skin being lapped on the ends, as though the globular skin had been formed in sections. 151