L92 CEYLON PEARL OYSTER REPORT. 



granular nature (figs. 5, 7, g.). This substance is highly refringent and, as above 

 mentioned, stains a pale reddish colour with hematoxylin and pale yellow with 

 picronigrosin. I thought at first that it might perhaps be muscular, but on further 

 examination it appeared to consist of rounded masses not fibrils, and at present its 

 nature and function seem to lie quite uncertain. It does not appear in the basal 

 portion of the papilla, but commences about halfway up the stem, and is most 

 abundant in its distal portions and in the stouter branches, where it sometimes 

 occupies quite a large proportion of the transverse section (fig. 5, g.), and I think it is 

 the cause of the yellowish appearance of the apex mentioned above. It extends in 

 gradually decreasing amount along the branches, but ceases some distance from the 

 tips (figs. 7 and 8). Towards the tips of the branches the various component tissues 

 gradually disappear, leaving only the connective-tissue and epithelium (fig. 8). 



The epithelium covering the papillae (figs. 1 to 9, ep.) consists of a single layer ot 

 cells, and is about 0'02 millim. in thickness. The cells are of rounded quadrangular 

 outline and have large spheroidal nuclei. 



In relation with the epithelium are certain peculiar spherules (Plate III., figs. 9 to 13), 

 the nature of which seems to me very problematical. There are between 15 and 'JO 

 of these arranged in a ring around the stem of the papilla quite close to its base. 

 They are irregularly placed, sometimes in a single row, sometimes in two, and 

 they vary in diameter from - 034 millim. to 0'05 millim. Very few of them come to 

 the surface, and I was unable to find any trace of them by surface examination. I 

 am inclined to think that the different appearances presented by these bodies indicate 

 developmental stages, and I will therefore first describe what seems to be the most 

 complete form. 



The central part of the organ consists of a cylindrical plug (tigs. 9 to 13, p.), the outer 

 end of which is almost on a level with the surface of the epithelium, the other 

 extremity penetrating somewhat below it. The outer end is slightly convex, the 

 inner appears to merge gradually into the tissue beneath. In transverse sections the 

 plug is oval, the diameters being 0"03 millim. anil 0"0l!5 millim. ; the length of the 

 plug cannot be measured exactly, owing to its fusion with the other tissues at the 

 lower end, but it may be taken at about 0'035 millim. The composition of this plug 

 is faintly granular and almost homogeneous ; it shows traces of breaking up here and 

 there into fragments by transverse lines, but this is probably an effect of shrinkage. 

 Below the plug and sometimes apparently rising up around it is a mass of tissue 

 of a flattened spheroidal shape (to.). The plug fits into a depression in the outer 

 surface of it, and its lateral expansions support the superficial epithelium. In the 

 only longitudinal section I have of one of these structures (fig. 10) the diameter of 

 this lower portion is 0'0G5 millim., and its depth below the epithelium 0"021 millim. 

 approximately. In this longitudinal section it appears granular and faintly stained 

 like that of the plug, but there is a distinct tendency for the granules to be arranged 

 in layers (figs. 10, 11, in.). In sections at right angles to this the structural arrangement 



