MORPHOLOGY OF LAMELLIBRANCHIATE MOLLUSKS. 433 



- Plate LXXXVI— Continued. 

 Area (Aryina) pexata : 



Fig. 50. Single gill filament, il, inner lamella ; ol, outer lamella ; ifc, interfilamentar connection. 

 Cardita borealis : 



Fig. 51. Vertical, transverse section in region of ])e(lal ganglion ; />■, stomacli ; /, liver; </, generative 

 mass; ig, inner gill; j^p, posterior palp; me, mantle edge; pij, jjedal ganglion, with cerebral 

 commissure running dorsally. 



Plate LXXXVII. 

 Toldia limuliila : 



Fig. 52. Removed from shell; right mantle fold dissected oti'; aa, anterior adductor; jya, posterior 

 adductor ; I, liver mass and generative gland, on the surface of which may be seen the lof)p of 

 the intestine, i; p, large palp, extending beneath visceral mass. At its posterior end springs 

 the appendage ap; g, gill, extending from posterior end of palp to base of siphons, s; me, 

 mantle edge; /, foot; d, ventral disc of foot. 



Fig. 53. Transverse section across sijihou of Yohlia, showing portion of wall of anal, on, and bran- 

 chial siphons, br, including a jtortion of siphoual septum, s.s; c, covering of exterior of 

 sijihons; it is more or less transparent, contains numerous nuclei, and, at places, indications 

 of elongated cell boundaries; trm, regularly arranged bundles of transverse muscles in walls 

 of both siphons and sii^honal septum; Im, numerous bumlles of longitudinal muscles (here 

 cut transversely), alternating regularly with the transverse layers. 

 Ontrea virginiana — Oyster : 



Fig. 54. Portion of secretory epithelium of uephridium in Ostrm; exc, excretory cells, with deeply 

 stained bases and transparent globular free ends; ?, lumeu of excretory tube, into which 

 break off fluid globular ends of cells. Many of these contain a small stained body. 

 Mactra solidisshna : 



Fig. 55. Crystalline style. End teased off in spiral from softer central axis, c«. 

 I'ecten irradians — Scallop : 



Figs. .56 and 57. Concretions showing concentric structure, from excretory cells of nephridium. 



Fig. 58. Excretory cell from uephridium; con, distally placed concretion (these all show a deeply 

 stained central portion of various shapes and sizes); vac, numerous small vacuoles; nuc 

 nucleus. 



Fig. 59. Elongated cells from same, containing numerous spherical vacuoles of varying sizes. 



Fig. 60. Segmenting eggs found in nephridium. 

 Soleiiomya velum : 



Fig. 61. Single siphoual opening in mantle. A, walls not bent ; B, walls bent to form upper, as, 

 and lower siphoual openings, hs; t, tentacles. 

 Ostrea virginiana — Oyster: 



Fig. 62. Transverse section of palp of Ostrea, near ventral or outer edge. Inner surface thrown 

 into ciliated ridges or folds, /. In this region these consist of two secondary folds, ■■</; ct, 

 irregular membrane at base of folds; fc, fat cells. 



Fig. 63. Same, midway between ventral edge and liase, showing difference in character of folds, /. 



Fig. 64. Same, at base. No secondary folds. Supporting tissue at base of folds much thicker, ct; 

 iv, blood vessel. 



Plate LXXXVIII. 



Ostrea rirginiana — Oyster : 



Fig. 65. Striated muscle fibers in auricle of heart; smf, striated muscle fibftrs, generally, if not 

 always, attached to thick, homogeneous, supporting membrane of wall, sm; a, protrusion 

 of supporting membrane through epithelium of wall to exterior; pgc, pigment cells; i", 

 vacuolated epithelial cells scattered throughout muscle fibers. 

 A rca {Argina) pexa ta : 



Fig. 66. Cross-section of gill filaments; glc, gland cells; If I, cilia of straining line; ch, chitin; 

 cj, ciliated junction; /, frontal epithelium; vs, vascular s])ace between walls connecting 

 lower part of descending and ascending filaments. This filament was cut lower down than 

 the other three represented in the figure (see Fig. 50). 



F. C. B. 1890—28 



