BY S. J. .TOHNSTOK. 347 



In the meantime, the fertilized ovum has entered the ootype, 

 and moves towards the entrance of the yolk-duct. Mostly the 

 ovum moves up to that point and awa}'^ again several times, but, 

 finally, a number of yolk-cells (generally four) enter the ootype, 

 and at once become fastened to one side of the ovum, so that 

 this cell noM^ forms the apex of a little group of five cells. The 

 walls of the ootype now undergo movements which roll the form- 

 ing egg about, as one might roll a ball of putty between the 

 hands. In this way, the egg becomes shaped, and a shell 

 appears. This forming shell is, at first, so transparent as ap- 

 parently to l)e invisible, for when I have first been able to see it, 

 it has already attained some thickness, and gradually becoming 

 less transparent, it thus becomes more easily discernible. Unfor- 

 tunately, I have not yet been able definitely to observe the shell 

 being actually formed out of those globules in the yolk-cells, 

 which Goldschmidt and others state(26) furnish the material of 

 the shell; but I am convinced that I can confirm Goldschmidt 's 

 observations, for the reaction of the newdy formed shell and of 

 the globules in the yolk-cells to stains like safranin, for instance, 

 which gives the most favourable results in this regard, is identical, 

 while there is nothing in the "shell-glands" that becomes stained 

 in the same way. 



The shell having become formed, the egg is passed on to the 

 uterus, and another oosperm takes its place in the ootype. 



From the foi-egoing, it will be seen that, in this species at least, 

 the function of Laurer's canal is to get rid of the sperms that 

 have tried and failed to effect an act of fertilization, as contended 

 in general by Looss(47, 48), Benham(2, p. 88), Goto(27, p. 174). 

 It may also get rid of unused yolk-material, for, though I 

 have not actually seen any in the canal itself, I have seen, near 

 the opening of the canal on the exterior, little accumulations of 

 objects that look like pieces of broken-up yolk-cells. From the 

 study of another trematode, Distomum pristwpJi.ori,{Z'l), I was 

 formerly of (jpinion that Laurer's canal functioned as a vagina, 

 for this canal, in that worm, was fairly wide, and possessed well- 

 developed muscular walls, and, furthermore, was filled with 

 sperms. It could quite well be, of course, that these sperms were 



