34 OSBORN. [Vol. XVIII. 



tion of the oviduct at the genital aperture the epithelium so evident 

 elsewhere in the passage changes to cuticle and is continuous with 

 that of the general surface of the body. The oviduct receives only 

 one duct, that from the yolk receptacle, which enters it at a point 

 very near to the ovary. In many trematodes a duct opens into the 

 oviduct between the entrance of the yolk-duct and the ovary, the 

 Laurer's canal. I have examined this region very carefully with- 

 out being able to recognize any indication of such a passage in 

 Cotylaspis. Laurer's canal is somewhat rudimentary in Aspido- 

 gaster, where, in the mature form, its outer end does not open to 

 the exterior as in trematodes generally, where it is present, and it 

 is stated by Nickerson to be absent in Stichocotyle, and is absent 

 from Cotylogaster* Laurer's canal at best seems to be a very 

 variable structure, opening in some cases to the exterior, in other 

 cases to the intestine, in still others ending blindly and in still 

 others being .wholly absent. It is present in one species and absent 

 in another closely related one, e. g., in the genus Distomum. 



This location of the vitellaria is shown in Fig. 3. They are made 

 up of a comparatively small number of flask-shaped follicles, all of 

 which lie so as to open toward the center of the body. The follicles 

 differ in number in different cases ; in nine different flukes I 

 counted them as follows: 70, y2, y6, 80, 84, 90, 105, no. They 

 are approximately equally divided between the right and left sides. 

 All of them underlie the diaphragm (see Fig. 7), and in this 

 regard are different from Aspidogaster, in which these follicles all 

 lie dorsal to the diaphragm. Stafford shows (Figs, ii, 12, 25) 

 their ducts piercing the diaphragm to communicate .with the rest of 

 the reproductive system which is under the diaphragm. The 

 ducts leading from the follicles are ordinarily invisible, but can be 

 demonstrated by making the yolk cells flow in them by pressure. 

 They lead to a right and left main duct, which at last enters the 

 yolk receptacle just in front of the spermary. The follicles them- 

 selves (Fig. 57) measure from .05 to .08 mm. in width and .08 to 

 .13 mm. in greatest length. Those of a particular animal are of 

 nearly the same size; possibly their difference of size in different 

 animals is due to functional conditions, but the cells in all have the 



* According to Monticelli, but Nickerson (Zool. Jahrb., XV., Syst., p. 

 611, 1902) finds it present in the American species C. occidentalis. 



