1911 J Watson: The Genus Gyrocotyle. 399 



spermatozoa, occasional deeply staining cells, large, and with 

 very large nuclei. These were noted and figured by Spencer 

 (1889, p. 146) : he suggests that they "may be simply the sperm- 

 blastophores from which the ripe sperm have separated^ but 

 there is no proof of this. ' ' The writer is convinced that they are 

 ova, which have entered the receptaculum seminis through the 

 duct which leads from this structure to the oviduct, the ductus 

 seminalis. The finding of these cells at the entrance of this duct 

 into the receptaculum and their resemblance to the ova, renders 

 this certain. 



The passage to the oviduct, the ductus seminalis, has a very 

 thick muscular wall lined with cilia and an exceedingly small 

 lumen, often completely obliterated in sections. For this reason, 

 Spencer was unable to demonstrate it to his own satisfaction, 

 though convinced that it must exist. 



The vagina passes forward, in the early part of its course 

 much convoluted and lying close to the receptaculum seminis. 

 Further forward it lies in the parenchyma close to the dorsal 

 wall of the uterus ; it turns ventrally near the middle of its course 

 and passes gradually to the ventral surface, where it finally 

 opens, laterally and posteriorly to the penis, near the right 

 margin of the body. The lumen of the vagina is lined with a 

 layer similar to that described for the receptaculum seminis, not 

 ciliated. It is not epithelial, as described by Lonnberg. Its wall 

 is composed of a thin layer of longitudinal muscle fibres ; it is 

 embedded in parenchyma and lies within the main mass of longi- 

 tudinal muscles, close to the wall of the uterus. As the vagina 

 nears the anterior margin of the uterus its lumen increases in 

 diameter. During its course past the convolutions of the vas 

 deferens this increase continues, and its wall is also increased in 

 thickness. The lining of the tube becomes much convoluted 

 in its course toward the left margin, and increases suddenly in 

 diameter in the latter half of its transverse course, opening 

 finally by a large aperture with much-folded margins and heavy 

 muscular wall. This region is plainly adapted to copulation. 



The testes are arranged in two groups not connected and not 

 symmetrical (pi. 39, fig. 42). The left testis extends from the 

 posterior border of the anterior third of the body, forward to 



