522 J. PERCY MOORE. [Vol. X. 



with the longitudinal muscles. Around the mouth of the bursa 

 they form a sphincter, but elsewhere a thinner layer one fibre 

 deep. This is interrupted in the upper part of the copulatory 

 bursa by the enormous enlargement of two lateral groups of 

 epithelial cells to form the bursal glands, which push between 

 the two muscular layers and occupy what corresponds to the 

 spaces between the longitudinal and circular muscles of the 

 body walls, bulging the side walls of the bursa outwards, so 

 that the transverse diameter is fully one-half greater than 

 the antero-posterior (Figs. 19, 20, 24, and 26). The circular 

 muscles thus lie entirely within the bursal glands, between 

 these and the lumen of the bursa. 



In the penis sheath (Figs. 19 and 20) the circular fibres 

 become still further distinct from the epithelium, and closely 

 connected with the longitudinal muscle coat; leaving a nearly 

 empty space all around, between the epithelium and the circu- 

 lar muscles. Numerous small muscular slips, from the circu- 

 lar fibres, traverse this sub-epithelial space and insert among 

 the epithelial cells. For the sake of clearness these have been 

 omitted in the partly diagrammatic Figs. 19 and 20. These 

 fibrils, which must be capable of great extension, are an im- 

 portant factor in the eversion and retraction of the penis. At 

 the constriction of the penis sheath above mentioned the sub- 

 epithelial space ceases (Figs. 19 and 20), and the circular 

 muscles come in direct contact once more with the epithelial 

 cells. They extend together beyond the limit of the longitu- 

 dinal muscles, and expanding, form a prominent vesicle (Figs. 

 19 and 20 sv^) which receives the glandular sperm sac, and into 

 the cavity of which the lumen of the penis expands. The 

 muscle fibres of the atrium (Figs. 24 and 26) possess rather 

 elongated nuclei, and differ somewhat in minute structure 

 from those of the body walls, being rather a transition form 

 between these and such as cover the spermatheca. The 

 fusiform shape which Fig. 26 shows is due to oblique section. 



The epithelial portion of the invagination is derived from a 

 cellular zone of the epidermis, and undergoes no change 

 throughout the greater part of the bursa, except in the dorsal 

 region, where a pair of conspicuous glands are developed, one 



