longitudinal and an interior circular, lying near the ejaculatory canal 

 (Fig. 95); the space between the musculature, the outside of the exterior 

 membrane and the epithelium of the canal is filled by cells of the connecting 

 tissue. 



The second type of copulatory organ among monogenetic trema- 

 todes is represented entirely by a chitinous formation lying in a special 

 envelope, and provided with separate muscular retractors (for instance, 

 Dactylogyridae, Fig. 9S). Without doubt, this type of copulatory organ 



Fig. 96. Chitinous copulatory organs of different shapes, Dactylogyrus spp. 

 Drawn at different magnifications. 



originates from the chitinous armature of the pear-shaped organs of the 

 free living flatworms as is the case among Turbellaria (Beklemeschev, 

 1937). The ejaculatory duct among corresponding forms is practically re- 

 placed by a special chitinous pipe into the base of which enters the ejacula- 

 tory duct and the glandular ducts --prostate and granule -forming. The for- 

 mation of the pipe is mostly widened and the ejaculatory duct forms a widen- 

 ing seminal vesicle in its cavity. The pipe itself is of varying shape and 

 length. Annong some forms it is almost straight and broad, in others it is 

 thin, sometimes very long, curved, and twisted completely or partially as 

 a spiral, etc. In certain cases the diameter of this pipe, which plays — 

 generally speaking, the role of the penis, changes along its extension very 

 significantly, now narrowing itself toward the free end, now widening. 

 Usually in addition to the pipe there is a special chitinous complex support- 

 ing it which is sometimes very intricately formed. The structure of the 

 supporting apparatus and the pipe itself has a great significance in the 



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