36 BULLETIN OF THE 



folds. It is lined with an epithelium of elongated cylindrical or pyriforra 

 cells of a glandular nature. The appearance of the cells varies with the 

 activity of their secretion ; the protoplasm may be either homogeneous, 

 or filled with oil-like globules, or it may be vacuolated. The cells rest 

 upon a fine basement membrane. There is no musculature, and there 

 are no cilia. 



The mouth of the uterus is prolonged into a tube with thick muscular 

 walls, the vagina (Plate IV. Fig. 42, vag.), which runs backward, pass- 

 ing above and to the left of the penis and then dipping down toward the 

 ventral side of the body, where it opens into the genital atrium. Where 

 the vagina arises from the uterus it is lined with a ciliated epithelium 

 of low cubical cells, and possesses a musculature of circular and longitu- 

 dinal fibres. As it passes backward, the cells of the lining epithelium 

 become taller and cylindrical (Plate II. Fig. 15, eHh.), and the nuclei are 

 elongated. The outer ends of the cells show distinct granulations, and 

 the contour of the lumen becomes uneven ; the glandular nature of the 

 cells now becomes apparent. Along with the change in the appearance 

 of the cells of the lining epithelium there is an increase in the thickness 

 of the musculature, which now consists of alternating layers of circular 

 and longitudinal fibres. The musculature of the vagina reaches its great- 

 est development at the point where it bends toward the ventral side of 

 the body ; from this point onward the cells lose their glandular char- 

 acter, and the musculature diminishes in thickness, till, at the point 

 where the vagina receives the oviducts, it again consists of only a single 

 layer each of circular and longitudinal fibres. Moseley ('74, p. 141) and 

 lijima ('84, p. 420) speak of radial fibres in the walls of the vagina; but 

 I could not find any. 



The accessory female organs of Triclads have been the subject of 

 much discussion. There are no other structures about which so many 

 opinions at variance with each other have been advanced. The organ 

 which I have called the uterus is regarded by lijima ('84, p. 419) as a 

 simple gland whose secretions go to form the cocoon. In his opinion, it 

 has no function in connection with the union of the sexual elements ; he 

 considers it homologous with the shell gland of Cestodes and Trematodes. 

 According to Kennel ('88, p. 458), it is to be considered as a receptacu- 

 lum seminis, and its secretions serve to preserve the spermatozoa. Hallez 

 ('87, p. 24) maintains that fecundation takes place in the uterus, and 

 tliat in it the yolk cells join the egg cells. According to Hallez, there is 

 a division of labor among the cells lining the uterus. The majority of 

 them secrete the substance of the cocoon, others secrete " uu liquide 



