226 PROP. W. A. HERDMAN ON THE STETJCTUBE OF 



Note on some Points in the Structure of the Gill of the Ceylon 

 Pearl-Oyster. By W. A. Heedman, F.E.S., President. 



[Eead 3rd November, 1904.] 

 (Plate 27.) 



In examining the structure of the gill in Margaritifera vulgaris, 

 Schnm., for the purposes of my Eeport on the Ceylon Pearl- 

 Oyster Fisheries, I have corae upon two little points which may 

 be of sufficient interest to be put on record * . 



The first of these is the pi-esence of extensive ciliated junc- 

 tions (1) in the median line between the inner gills of the two 

 sides, and (2) laterally between each outer gill and the mantle- 

 lobe. 



In examining the living pearl-oyster the inner gills seem to be 

 nnited in the middle line, and the outer gills seem to be joined 

 to the mantle outside them. In dissecting a well-preserved 

 specimen, where there has been no marted contraction or dis- 

 tortion, the same apparent continuity is seen. Concrescence of 

 these originally separate parts seems to have taken place as in 

 many other Pelecypoda, such as most of the Eulamellibranchia. 

 On manipulating the gills, however, it is found that slight 

 pressure with dissecting-needles is generally sufficient to force 

 the parts asunder, and they are seen to separate with clean-cut 

 broad edges or seams and leave no appearance of tearing. 

 Figure (Pi. 27) 1 is a diagrammatic transverse section of both 

 ctenidia (the four " gills "), and the darker lines at M.c.j. and 

 L.c.j. show the junctions in question. Figure 2 is a dissection 

 of the right ctenidium separated at M.c.j. from its fellow of the 

 other side and at L.c.j. from the mantle, so as to show the 

 broad seams. 



Transverse sections (such as figure 3) through the gills and 

 mantle show that the explanation of these adhesions, and yet 

 ready separation, is that the seams in the case of both gills and 

 mantle-lobes are covered with short stiff cilia which interlock to 

 form very effective and extensive ciliated junctions. Figure 4 

 shows the median one between the upturned ends of the inner 

 lamellae of the inner gills. The gap in the centre is probably a 

 post-mortem separation of the two epithelial layers. Figure 5 

 shows the lateral junction between the reflected or outer lamina 



* They are briefly referred to in Part II. of the Eeport to the Ceylon 

 Government (Eoyal Society, 1904). 



