30 ART. 4. — EKITAIIO NOMURA : 



muscle and the glandular cell layer of the atrium. Each lobe of 

 the gland is surrounded by a thin connective tissue layer, which 

 is a direct continuation of that of the atrium. 



e. Duct portion of the atrium. The duct portion is about 

 half as long as the atrium. On the side of the atrium, the canal 

 is only 20 /^ in diameter, and the inner epithelium becomes thin- 

 ner and ceases to be glandular, the cytoplasm becoming compact 

 and the cell membrane distinct. After a further diminution of its 

 diameter, its epithelium is finally continued into the inner lining 

 epithelium of the penis. The outer two layers — muscle and con- 

 nective tissue — are the direct continuations of those of the atrium 

 and of the same structure. 



/. Penis and related portions. The penis is the direct 

 prolongation of the duct portion of the atrium enclosed in a 

 chitinous sheath and situated in the penial chamber, formed by 

 the invagination of the body wall. 



The wall of the penis consists of two layers. The epithelial 

 cells of the inner layer contain very little cytoplasm adhering to 

 the cell wall. The outer layer is a direct continuation of the 

 lining epithelium of the penial chamber and is folded on itself at 

 the proximal or posterior end of the penis. This layer gradually 

 diminishes in thickness for some distance as it proceeds towards 

 the distal end of the penis and is flattened out into an exceed- 

 ingly thin membrane, but resumes its thickness and cellular con- 

 dition toward the distal end, where the penis is slightly enlarged. 

 The cells are perfectly similar in structure to those of the inner 

 epithelium. 



The chitinous sheath is attached to the hindmost end of the 

 penial chamber, and measures about 35 /* in diameter. The sheath 

 proceeds straight forwards with decreasing diameter (22 p) ; but 

 near the distal end it again becomes thicker and after a slight 

 curvature towards the median plane it terminates with a sudden 

 expansion and deflection. The wall of the chitinous sheath 

 is 2.3-2.5 /* thick, except at the deflected part where it is 

 thinner. 



