328 DR, H. LYSTER JAMESON ON 
Pl XXXVITITI. fig. 19 shows a group of such pearls, scattered 
among which are hypostracum-pearls (hy.p.). The nucleus of 
the eccentric pearl at nz.’ is clearly composed, like that of the 
incipient pearl shown on Pl. XXXIX. fig. 22, nac., of hypo- 
stracum, and resembles the hypostracum-pearl shown at fig. 21, 
which has a small quantity of granular contents. One of the 
columnar nuclei is shown enlarged at fig. 20. This is the nucleus 
of the large pearl shown in the upper part of fig. 19 
(Pl. XXXVIII,). Centrally there is a small ae in which a 
gr anular mass of doubtful origin is noticeable (g7.). This cavity 
is surrounded by an irregular zone of substance which seems to 
be the same as the amorphous repair-substance of the shell 
(cf. Pl. XL. fig. 29). Externally to this there is columnar 
substance, forming a sort of spheerocrystal-like mass, the fibro- 
crystalline calcium carbonate being deposited in a conchyolin-like 
basis, which, on decalcification of the pearl, remains as a 
framework. This substance is seen cut tangentially at one end 
of the pseudo-nucleus. Outside this is the normal nacre of the 
pearl. In one or two cases the amount of granular matter in the 
centre of the pearl was considerable ; thus Pl. XL. fig. 24, which 
is taken from the same series as the preceding figures, shows the 
central portion of a pearl which has a dumbbellwshaped double 
nucleus, the larger half being about +17 mm. in diameter, and 
each half containing an opaque brownish mass of dead animal 
matter, perhaps of cellular origin, but quite unrecognisable. The 
contents of the two cavities were continuous at one point. There 
is nothing to suggest that either of these bodies represented a 
dead Cestode; I could find no denser portion, such as would 
eee occur at the point representing the myzorhynchus, nor 
vas there anything that could be safely identified as the cuticle 
of the parasite. If the contents suggested anything, it was rather 
the remains of a large Protozoan “parasite, containing spore-like 
bodies in a plasma. (il xe the Sporozoan spores which Dubois claims 
to have identified in the nucleus of a pearl from J/. vulgaris from 
the Mediterranean, 7, p. 311, and 8, p. 104); or, perhaps, a mass 
of mucus containing a few cells. Each of ee centres was 
surrounded immediately by the amorphous substance, this being 
followed by, and continuous with, a radially calcified layer, the 
bases of the calcareous prisms being evidently embedded in the 
amorphous substance, which extended up between them to form 
the organic framework of the columnar substance. This condition 
is comparable to that seen at t. on Pl. X LI. fig. 30, which shows 
the amorphous substance secreted at the junction of two pearls 
in a compound pearl, passing over into columnar repair- 
substance. 
Externally to the columnar layer of the pseudo-nucleus the 
normal nacreous layers of the pearl are formed, 
The other extreme is shown on PI. XL. fig. 25,a hypostracum- 
pearl ‘08 mm, in diameter, the central cavity of whick has no 
contents whatever. 
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