POLYCLAD FLATWORMS — ^HYMAN 559 



and around the central organs (pharynx, copulatory apparatuses). 

 Sections show that these dots are located in the mesenchyme and are 

 aggregations of minute black granules. Similar dots are recorded for 

 P. langii (Laidlaw) (1902) and P. rotumanensis Laidlaw (1903a). 

 There is a pair of elongated tentacles situated far back from the 

 anterior margin. At the base of each tentacle is a circle of densely 

 placed eyes and between the tentacles are two cerebral groups of 

 eyes, of 20-25 eyes each (fig. 5c). The rounded ruffled pharynx with 

 central mouth is medially located, slightly anterior to the body 

 center. Behind it appears the copulatory apparatus, of which the 

 main parts are easily seen because of the transparency of the body. 

 There are seen (fig. 5d) the round spermiducal bulbs with thick 

 muscular wall of circular fibers to either side of the prostatic vesicle, 

 the cirrus sac with two large teeth, pyriform copulatory bursa extend- 

 ing anteriorly to one side of the male complex, and the vagina sur- 

 rounded with a halo of cement glands. The copulatory region was 

 removed and sectioned sagittally and the remainder of the worm 

 mounted whole. 



Copulatory apparatus: A sagittal view of the apparatus appears 

 in figure 6a. The rounded prostatic vesicle forms the anterior end of 

 the male apparatus; it has a moderately thick wall of muscle fibers 

 paralleling its external contour and a glandular interior composed of 

 glandular folds projecting into the lumen and composed of eosi- 

 nophilous granules. The two accessory prostatic vesicles or pockets 

 found at the posterior side of the main vesicle and very definitely 

 marked off in some species, notably P. oligoglena, are here poorly de- 

 fined, although apparently present. A wide prostatic duct leaves the 

 prostatic vesicle and receives at once a relatively long common sperm 

 duct into its ventral side. The spermiducal bulbs as they approach 

 the prostatic vesicle have a firm muscular coat of circular fibers that is 

 much thicker on the side towards the vesicle and soon becomes incor- 

 porated into the muscular coat of the latter. Each spermiducal bulb 

 then narrows to a sperm duct, still with a coat of circular fibers, that 

 soon joins its fellow to produce the common sperm duct. The common 

 sperm duct enters the prostatic duct from below just as the latter 

 leaves the prostatic vesicle. The right spermiducal vesicle does not 

 coil extensively in front of the bursa as it does in P. oligoglena. 



The prostatic duct with ciliated epithelial lining, thin but muscular 

 dorsal wall, and thicker muscular ventral wall, curves posteriorly 

 above the anterior part of the cirrus sac and enters the dorsal wall 

 of this sac at about its middle. The cirrus sac is an oval body with 

 excessively thick muscular wall. The muscles run mostly at right 

 angles to the external contours but actually a web of fibers is present. 

 Into the lumen of the anterior part of the cirrus sac there projects a 



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