70 OPISTHOBRANCHIATA OF BRAZIL 



mm., its greatest breadth 3.0 mm. and thickness 2.0 mm. Its 

 surface is very finely lobulated. 



Vas deferens and penis. The vas deferens courses straight 

 forward and outward along the inner and anterior faces of the 

 complex to the penis. Throughout its whole length it preserves 

 a uniform diameter of 0.5 mm., dilating suddenly at its outer 

 end into the penis. The penis is somewhat contracted and nearly 

 spherical in form, about 2.25 mm. in diameter, the large conical 

 glans (PI. XII, fig. 65, p.) projecting externally. The latter is 

 bluntly conical, its apex truncate, 2.0 mm. in length, i.o mm. in 

 diameter at the base, and tapering to 0.5 mm. at the apex. The 

 glans bears an armature of minute hooks, set in longitudinal 

 rows, about 17 in number near the distal end of the glans and 

 increasing to nearly 100 toward the base. The individual hooks 

 (PI. XII, fig. 64, a, b) are rather stout, the largest occurring near 

 the base of the glans, and measuring 0.02 to 0.027 mm. in height, 

 their basal dimensions being nearly the same. 



Vagina and duct. The vagina and vaginal duct lie upon the 

 upper anterior border of the anterior genital complex (PI. XII, 

 fig. 65, vag.), and are of about equal length. The distal vaginal 

 portion is conical, thick walled, with a series of longitudinal ridges 

 upon its external surface, separated by shallow grooves, united 

 at intervals transversely, giving the surface a somewhat lobulated 

 appearance, which is due to internal glandular structures. In 

 sections through the vagina and its duct the wall is seen to be 

 made up of two conspicuous layers, an outer muscular one, con- 

 sisting mainly of fibres arranged in a circular direction, and of 

 nearly uniform thickness, throughout the whole length of the 

 vagina and its duct, varying but slightly from about 0.045 ^^^ 

 An inconspicuous submucous layer of connective tissue bears 

 the innermost coat, the mucous layer, which is made up of a 

 layer of columnar epithelial cells, distended with secretion prod- 

 ucts. This mucous layer is thrown into closely crowded leaf- 

 like longitudinal folds, about twenty in number in the proximal 

 portion of the vagina, and increasing to some fifty or more in the 

 distal extremity. These folds range in height from 0.09 mm. 

 to 0.24 mm. in the proximal and distal portions respectively. The 

 narrow central lumen, left free from the folds, is filled with a 

 coagulated mucous-like secretion. 



