no. 3638 TURBELLARIA — KAWAKATSU 13 



pharynx to that of the penis bulb. A sagittal view of the copulatory 

 apparatus is shown in figure 4. 



The genital pore opens immediately into two cavities, i.e., anteriorly 

 into the male antrum containing the penis papilla and posterodorsally 

 into the duct of the copulatory bursa. There is no division of the 

 genital antrum into a common antrum and a male antrum (fig. 4). 

 The opening of the common ovovitelline duct is situated in the roof 

 of the terminal part of the male antrum. Terminal portions of the 

 ovovitelline ducts and the common ovovitelline duct receive numerous 

 glands, the secretion of which becomes a deep red when stained with 

 eosin. The wall of the male antrum is lined with a cuboidal epithelium; 

 the epithelium of the male antrum on the dorsal side is taller and more 

 glandular than on the ventral. Under the epithelium there are two 

 muscle layers, one circular and the other thick and longitudinal. 



The penis consists of a large spherical bulb and a moderately large 

 conical papilla; the bulb is very muscular. It consists of the usual 

 mesh of muscle fibres taking a curved course paralleling the contours 

 of the bulb. The penis bulb is pierced by numerous eosinophilic gland 

 ducts that open into the bulbar cavity; these are seen easily in sec- 

 tions stained with Delafield's haematoxylin and eosin. The distin- 

 guishing feature of this species is the division of the bulbar cavity 

 (seminal vesicle) into a pair of moderately wide, oval-shaped cavities 

 in the penis bulb (fig. 4). The two continue to a narrow ejaculatory 

 duct in the penis papilla. 6 Both the bulbar cavity and the ejaculatory 

 duct are lined with a glandular epithelium of very tall cells, tapering 

 in thickness toward the tip of the penis papilla. The two sperm ducts 

 penetrate the penis bulb from the anterolateral sides and each opens 

 into a cavity of the seminal vesicle. 



The penis papilla has a slender and symmetric conical shape (fig. 

 4) . It is covered with a tall epithelium similar to that lining the male 

 antrum, under which there are two muscle layers, tapering in thick- 

 ness toward the tip of the papilla: a layer of circular fibres containing 

 a dense fibrous material next to the epithelium and a second layer of 

 longitudinal fibres. The ejaculatory duct opens at the tip of the papilla. 



The copulatory bursa is a large sac closely fitted into the space 

 between the posterior wall of the pharyngeal chamber and the penis 

 bulb (fig. 4) . It has a narrow lumen and the internal wall is lined by a 

 tall glandular epithelium. The bursa stalk runs posteriorly above 



6 In sagittal sections of the copulatory apparatus, the two parts of the separated 

 bulbar cavity appear as if they are situated above and below the penis bulb 

 rather than on either side of the midline of the bod3^. This condition, however, 

 seems to be the result of a postmortem muscular contraction, with a consequent 

 listing to the side of the dorsoventral axis, through which the material was 

 sagittally sectioned. 



