MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 147 



NIDAMENTAL GLAND. 



Immediately in front of the preanal papilla' of the female a large pleated gland is .situated 

 upon the inner side of the mantle. (Fig. -4, N.) This has been railed the nidamental gland. In 

 the fresh condition it is of a light yellow color, but when preserved its color is a dark brown. 



The nidamental gland extends across the mantle nearly the entire distance between the bases 

 of the anterior gills. It has been called kidney-shaped. It is shaped as a number of thin, closely 

 pressed, parallel folds would be if their ends were bent around close to their middle portions 

 until the opposite ends nearly meet each other. Most of the folds of the gland are thus continu- 

 ous around the curved ends of the organ. The infolding has taken place toward the anterior side 

 of the main portion of the gland. The gland is about 60 millimeters in width, and 25 millimeters 

 to 32 millimeters in length. At its edges the mantle is raised, forming a border entirely around 

 the gland. On the posterior side and between the anterior and posterior portions of the gland 

 the border thus formed is only a low ridge. Upon the ends and the anterior side of the 

 gland the raised mantle forms a fold which overlaps more than half of the inturned portions of the 

 gland. The outer surface of the ridge of the mantle is smooth, and the inner surface as well of 

 tlie overlapping anterior parts. The inner surface of the other parts of the border is ridged per- 

 pendicularly and is apparently covered by an extension of the glandular tissue of the gland. 



By means of the raised border of the gland a canal is formed which enters the anterior side 

 of the gland and branching, extends to each side between the anterior and posterior portions of 

 the gland. Owen suggests that the divisions of the nidamental gland serve " both to conduct the 

 secretion nearer the orifice of the oviduct, and also to prevent its being drawn within the respi- 

 ratory currents of water, and so washed away as soon as formed." If the channel between the 

 different portions of the gland serves to conduct the secretions of the gland, it is difficult to see 

 how it conducts them near the orifice of the oviduct with its open end directed away from the 

 oviduct and its lateral branches ending under the overlapping border of the gland. 



The parallel glandular folds of which the organ is composed are quite separate in the anterior 

 portions, but are grown together closelj T in the posterior portion. 



Medianly, between the ends of the anterior portions of the gland, is a thickened, apparently 

 glandular, projecting portion of the mantle. In the center of this is a low, longitudinal ridge. 

 (Fig. 4, Y.) 



The gland is supplied with blood through branches of the branchial arteries. A large blood 

 lacuna lies in the median, line in the mantle below the nidamental gland. This breaks up into 

 numerous smaller lacunae in the thickened portion of the mantle between the ends of the gland. 



In a half-grown female the nidamental gland was just forming. The mantle was scarcely 

 thickened, but the outlines of the different portions of the gland were already marked out by the 

 border formed by the raised fold of the mantle. The glandular area was covered by very fine 

 parallel ridges, scarcely visible to the naked eye. The gland was of the same color as the sur- 

 i - ounding portions of the mantle. 



Kerr has described a series of glands between the preanal papilla 1 and the posterior side of 

 the nidamental gland. The apertures, "to the number of about 150, form a band about 0.5 

 millimeter in width, curving gently forward on either side of the postanal papilla, tapering off 

 and terminating close to the advehent vessel of the posterior gill. In section these openings are 

 seen to be the apertures of tubular ducts which pass inwards perpendicular to the surface for 

 some little distance and then break up into several blindly ending branches. These are lined by 

 involution of the surface epithelium, which, in the neighborhood of each aperture, increases to 

 about twice its thickness elsewhere, its cilia at the same time becoming long and powerful (0.03 

 millimeter in length). Once within the narrow aperture the lumen of the tube expands to about 

 0.05 millimeter in diameter, and the lining epithelium becomes shorter, the remainder of the 

 lumen being lined by comparatively short columnar cells, each with a round ellipsoidal nucleus." 

 In some females this area is greatly swollen, forming a single elongate gland. It is not possible, 

 then, to distinguish the separate apertures of the glands upon the surface. I have not yet been 

 able to determine if the glands in the bases of the preanal papilla? of the male are homologous 

 Vol. 8— No. 5 i 



