WATSON : ANATOMY OP OCHTHEPHILA. 285 



front end, where the large median area comes to occupy the whole 

 breadth of the sole. The upper surface of the hinder end of the foot 

 is darkly pigmented, the colour in some cases extending right across 

 it, while in other specimens it takes the form of a pair of broad lateral 

 bands passing obliquely downwards from below the mantle. 



The Pedal Gland, which opens above the front edge of the foot, 

 extends far back, embedded in the pedal muscles, though the top 

 of its anterior part is exposed to the body-cavity. It consists of very 

 numerous large gland-cells, of which the secretion stains blue with 

 haematoxylin, surrounding a central longitudinal duct. The gland 

 measures a little over '5 mm. in diameter, while the diameter of the 

 duct is about 'li mm., except close to the opening, where it becomes 

 much broader. Along the floor of the duct there is a pair of wide 

 longitudinal ridges, with a median groove between them, towards 

 which the gland-cells converge. On the outer side of each of these 

 ridges, in the angle between it and the side of the duct, there is a much 

 smaller longitudinal ridge, formed by a thickening of the epithelium 

 lining the duct, this outer pair of ridges consisting of tall narrow 

 columnar cells instead of cubical epithelial cells. The roof of the duct 

 shows some small longitudinal folds. 



Numerous small unicellular glands are present in the foot-sole. 



The Mantle-Edge is of a pale colour, excepting the upper part near 

 the respiratoi y opening, where it is often more or less tinged with grey. 

 It bears right and left body-lobes, as shown in Fig. 2 on Plate VI. 

 The right lobe is divided by a deep slit into an elongated portion, 

 which lies near the penultimate whorl, and a small, somewhat 

 quadrate portion lying below the respiratory opening. Two widely 

 separated left body-lobes are present : a little one situated at the 

 base of the aperture, and a larger one situated on the left side of the 

 respiratory opening, and having a small extension which arches 

 over the opening in the manner shown in the drawing. 



The Mantle-Cavity is long, and stretches round a complete whorl. 

 Its roof is thin and translucent, but part of it shows minute specks 

 of brown pigment. This pigment is chiefly concentrated to form a 

 brown patch near the mantle-edge behind the respiratory opening ; 

 but in some specimens it extends below the periphery to form a short 

 band pai'allel to and just behind the mantle-edge ; while it may also 

 extend backwards for a much greater distance as a faintly pigmented 

 zone between the rectum and the pulmonary vein. The remainder 

 of the skin lining the shell is unpigmented. 



The Vascular System. — The main pulmonary vein is large and 

 conspicuous. It receives some small branches towards its anterior 

 end, but these are not at all prominent and can only be seen under a 

 strong lens. Where the pulmonary vein passes beneath the anterior 

 part of the kidney, sections show that it receives a series of minute 

 vessels from the inner surface of that organ. Then, as it passes into 

 the pericardium, it receives three slightly larger branches, one from 



