326 DR, H. LYSTER JAMESON ON 



probably cine to variations in the rate of secretion of the con- 

 stituent substances. This zone is 0*03 mm. thick. The central 

 cavity is empty, except for a few granules. 



In this case the muscle-pearl, if such it is, does not contain a 

 pseudo-nucleus composed of hypostracum or a, sphserocrystal-like 

 body such as those shown in figs. 19 & 20; and v,he real 

 " nucleus " of such a pearl might be said to be a cavity which may 

 or may not contain a few indistinct granules, perhaps of foreign 

 origin. 



The same condition is also typical of those pearls which I have 

 examined from Dr. Kelaart's material. I have decalcified 38 of 

 these in all (PL XXXYII. figs. 14, 15, & 16 ; PI. XXXVIII. 

 figs. 17 & 18 ; PI. XLIV. figs. 46, 46 «, 47, 47 a, & 48). That these 

 pearls are of the same nature as the other muscle-pearls seems 

 probable from the fact that a few hypostracum-pearls occur mixed 

 with the other pearls in Dr. Kelaart's specimens, and from the com- 

 plete series of intergradations between the various forms described 

 above, which is shown by the unlabelled specimens in the British 

 Museum, desciibed below. PI. XXXVII. fig. 14 is a section of 

 Dr. Kelaart's specimen showing " pearls in ovary." Each of 

 these pearls lies in a cavity which doubtless was originally lined 

 w-'ith an epidermal epithelium, though this can no longer be 

 recognised owing to the state of preservation. The cavity is 

 surrounded in every case by a layer of the granular subepidermal 

 parenchyma (par.). Some of the pearls have been forced out of 

 the subepidermal layer, and now lie embedded in the deeper 

 connective-tissue, in which are seen muscle-bundles and tubules 

 of the ovary. 



In each case the centre of the pearl is a small cavity, containing 

 a few granules or strands of what appeai-s to be conchyolii:i ; but 

 the pearl in the lower right-hand corner contains also some 

 columnar substance. The irregular conchyolin-like n^atter is well 

 seen in the centre of the pearl in the top left-hand corner of the 

 sketch, which is shown enlarged in fig. 15. It is interesting to 

 note that the sei-ies of sections from which these drawings were 

 made contained an example of the smaller Cestode larva, Tylo- 

 cephcdum minus. 



Plate XLIY. figs. 46, 46 a, k 47, 47 a show two pearls 

 picked from one of Dr. Kelaart's specimens, decalcified, and 

 examined whole in oil of cloves (46 & 47) and after being sec- 

 tioned (46 a (fc 47 a). Fig. 46 shows a dense central mass, of 

 closely laminated nacreous substance, which on superficial 

 examination might be taken for the remains of a dead parasite, 

 but a section shows that the whole pearl is composed of nacreous 

 substance around a small central cavity. 



Fig. 47, examined Avhole, was extremely suggestive of a dead 

 parasite ; indeed, the concentric lamination of the pseudo-nucleus 

 was not disclosed till sections were cut. These (fig. 47 «), 

 however, furnished the explanation. The real centre of the 

 pearl was, as in the rest of Dr. Kelaart's material, a nacreous 



