7t» ^Ir. "W. Nicoll on the 



bifurcation. The cirnis-pouoli is \o\\'^ and narrow, extending 

 some distance behind the ventral sucker. It contains at its 

 j)ostcrii)r end a h\rj;c bipartite vesicnhi seminaHs, from the 

 anterior end of which issues the ductus cjaculatorius. The 

 latter bends back abnost innncdiatcly to be alongside the 

 vcsicula scniinalis, Ijut bending again it passes forward to 

 the penis. This organ is long and slender, and when well 

 extended is curved. It has a sqnarely-cut end, but instead 

 of being inflated at its termination, as Olsson represents it, 

 it is somewhat tapering. The configuration of the internal 

 genitalia is precisely as Odhner^ represents it.- 



In one ease I was fortunate enough to witness the fer- 

 tilization and formation of the ova. The worm was under 

 pressure, and the unfertilized ova passed along the oviduct 

 iairly rajjidly. As each arrived opposite the receptaculum 

 scminis, it was surrounded by sperms, and shortly afterwards 

 two or three yolk-plugs were congregated round it. The 

 mass was forced on towards the uterus, receiving as it went 

 a shell-coating and gradually acquiring the characteristic 

 elliptical shape. The whole process did not last longer than 

 ten minutes. 



The vitelline glands consist of numerous follicles, not 

 by any means so regular or so large as Odhner represents 

 them. He is correct in saying that they do not extend in 

 front of the ventral sucker, although occasionally a follicle 

 or two is to be found in the neck. 



The uterus is short and rarely contains more than 20-40 

 eggs ; Odhner says 20-30, and yet in his figure f he repre. 

 scnts upwards of 80 eggs. The ova are ligl»t yellow to 

 yellowish brown in colour, and measure, according to my 

 observations, 'OrS-OS^ mm. in length by O^O-'O.jI mm. in 

 breadth. These rather wide limits include measurements of 

 the ova from various hosts. The details in four cases are as 

 follows : — 



mm. mm. 



Trom Gasterosteus aculeatus .... -OZo-OSl x •040-044 



., Coftm bulmlis •07-')-08l x •044-0o4 



„ CentnuxAns ynnnellus .... 'OTo X OlO-'Oo^ 



„ Zoarces viciparus •031-084 X •040-'0o0 



Odhner's figures are •0G0-084 mm. x •010--045 mm. 

 The minimum length-limit seems rather small. I have 

 certainly never observed ova (mature, at least) ai)proaching 

 that small size. My measurements were usually determined 



* Loc. cit. pp. ol 0-511, pi. 33. f^g. 10. 

 t Loc. cit. pi. 33. fig. 9. 



