ZooL.— Vol. III.] HEATH— EPIDBLLA SQUAMULA. II7 



In the crypts thus formed the sperm occur in all stages of 

 development, which appears to closely follow the plan most 

 accurately determined by Goto ( 1895) , in Microcotyl caudata. 



The ducts leading from the testis (vasa efferentia), and 

 often funnel-shaped for a short distance, unite in the median 

 line with the vas deferens, which passes forward to the right 

 of the ovary, and after a tortuous course penetrates the wall 

 of the reservoir in which the secretion of the prostate glands 

 is stored. Traversing this, it finally opens into the cavity 

 of the penis near its base. Throughout its entire extent it 

 is invariably filled with sperm, and is also sharply separated 

 from the adjoining tissues by a sheath of apparently the 

 same character as that surrounding the testis. On the inside 

 of this investing coat in the terminal third of the vas defer- 

 ens is a series of ten or twelve cells, clear as crystal in life, 

 whose position is more accurately indicated in fig. 13, x. 

 In the region of the large spherical nucleus each cell projects 

 far into the lumen of the duct (fig. 4), but from this point 

 gradually becomes thinner as it extends around the wall or 

 to the point of contact with neighboring cells. 



Goto (1895) has discovered similar cells in the vas def- 

 erens of Microcotyl chiri and M. sctcBnce, and considers 

 them the remnants of the epithelial cells of which the vas def- 

 erens was originally formed. Nothing short of a study of 

 the development of these organs will settle such a ques- 

 tion, but there is no doubt that if they are remnants they 

 nevertheless serve some function in the mature worm. The 

 protoplasm of which they are composed is finely granular, 

 staining uniformly, and while there are some reasons for 

 considering them to be gland cells, there is nothing which 

 definitely determines their nature. 



Another set of problematical cells is situated behind each 

 testis in the angle which one makes with the other (figs. 7, 

 11), but whether they are associated in any way with the 

 reproductive system it is impossible to state. They are al- 

 ways four in number, perfectly transparent in living speci- 

 mens, and are composed of finely granular protoplasm, 

 usually vacuolated except in the immediate vicinity of the 



