1914] A New Cestode from A mi a Calva L. 103 



Female System. 



The vagina opens on the ventral surface of the proglottis imme- 

 diately behind the opening of the cirrus and from o . 02 to o . 07 mm., from 

 it (Fig. 17). While in most cases the aperture is circular in outline and 

 from 20 to 30/i in diameter, it is occasionally found in preserved material 

 to be transversely elongated, more especially when it approximates the 

 male opening (vide supra) . The first portion of the vagina is in the form 

 of a somewhat elongated vesicle, 56 jj, in transverse diameter and situated 

 beneath the vesicula seminalis; it is quite comparable, in shape at least, 

 to the " Scheideneingang " of Sommer and Landois. After being slightly 

 deflected dorsally, as in D. latus, the duct then passes back along the 

 ventral side of the uterus-sac, on either side of the median line, or crosses 

 from one side to the other at different levels ahead of the uterus-opening — 

 in young proglottides ahead, necessarily, of the limb of the uterus directed 

 towards the latter. In either case it turns to the median line again close 

 to the posterior wall of the uterus-sac, and then passes over the ovarian 

 isthmus and into the "generative space" where it expands, as it courses 

 ventrally again, to form a receptaculum seminis. 



The structure of the vagina is quite comparable, on the whole, to that 

 of the vas deferens. Posteriorly it is lined with a syncitial epithelium, 

 supported by an indistinct basement membrane which is relatively 

 somewhat thinner than that of the vas deferens of the same proglottis, 

 excepting in the region of the receptaculum seminis (vide infra). This 

 is doubtless due to the fact that during the period of differentiation of the 

 two tubes from the middle and narrower portion of the common anlage 

 of the genital ducts, the vagina is somewhat in advance of the vas defer- 

 ens, that is, it develops a lumen slightly previous to the formation of one 

 in the latter, and then, evidently keeps in advance of it during subsequent 

 growth and distension. From a point opposite the anterior end of the 

 uterus-sac to its opening the vagina is lined with a cuticle which in many 

 cases is lacerated and torn, especially at the surface next to the lumen. In 

 this region, at the proper stage, that is, about the time when only a few 

 eggs appear in the uterus-sac, what was considered by the writer to be 

 the transformation of the epithelium into the cuticle can be observed 

 much more clearly than in the case of the cirrus where only a compara- 

 tively short length of duct develops a cuticle. This seems to be brought 

 about almost wholly by the sinking of the nuclei into the surrounding 

 mass of cells derived from the outer layers of the anlage and lying out- 

 side of the basal membrane and circular muscles, and by the subsequent 

 alteration of the epithelial substance to form the homogeneous cuticle. 

 Very few nuclei in their passage through the membrane were seen, since 

 no lengthy study of this subject was undertaken and since, as suggested 



