STRUCTURE OF CLINOSTOMUM 217 



Continuing it anteriorly is a smaller portion whose wall is sup- 

 plied with a very strong coat of circular muscles. It is followed 

 by a less muscular portion at the outer end of the sack. This 

 portion is surrounded by what are apparently to be regarded as 

 prostate cells. This part is not as strongly muscular as the middle 

 region of the tube. Following the usual nomenclature I have 

 designated the middle and outer parts respectively as prostate 

 portion and ductus ejaculatorius. It seems however that the 

 more glandular part and the more muscular parts are out of the 

 usual order. Thus in D. isoporum (Looss, '94, fig. 104), the outer 

 part is strongly muscular, and coiled and between it and the semi- 

 nal vesicle there is a small chamber with which the large prostate 

 cells communicate. 



Testes. The testes are somewhat pyramidal in shape, their 

 bases slightly concaved and facing each other. In some cases the 

 remaining surfaces are more or less deeply indented, in many 

 others they are entire. A sharp line bounds the testes. The 

 vasa deferentia have a wall of epithelium with flattened nuclei. 

 This epithelium can be recognized in the wall of the testis where it 

 connects with the vas deferens but no epithelium can be seen in 

 the wall of the organ elsewhere. Apparently trematodes differ 

 on this point. In Cotylaspis (Osborn, '94, fig. 88) the wall of the 

 organ is- distinctly epithelial. Schwartz ('85) found nuclei in the 

 wall of the testis of certain early stages of trematodes while Ziegler 

 ('83) claimed that the wall is non-cellular in Bucephalus and 

 Gasterostomum. 



The testes are filled with cells which, in some bass worms, are 

 almost completely filled by the very large nucleus, poor in chro- 

 matin, and with a very large, readily staining nucleolus which 

 indicate the inactive stage preceding spermatogenesis; in other 

 bass specimens with cells showing various phases of spermato- 

 genesis. In the heron worms the testes contain fully developed 

 spermatozoa scattered among the active cells. 



Ovary. The size and form of the ovary as shown in fig. 26 of 

 Looss' paper ('85) is unlike anything which I have found in my 

 material, in which it is oval, entire and measures 0.4 mm. by 0.2 

 mm. In MacCallum's figure it is also small and entire. It is 



