LIFE HISTOEY OF THE LIVER-FLUKE. 105 



only l-30th part as long as the adult, and these immature 

 forms gave me valuable information as to the structures to be 

 expected in the cercaria, the relative size of its suckers, &c. It 

 was usually supposed that the sheep when grazing picked up the 

 parasites whilst they were still within the snail. This view 

 was upheld by so eminent an authority as Professor Leuckart 

 in a paper published in the beginning of 1882.^ But I had 

 already collected evidence from independent sources, which 

 inclined me to the belief that the larvae were picked up in 

 the encysted condition attached to the grass. Hence the pre- 

 sence of a special cystogenous organ in the cercaria, and its 

 habit of encysting on grass were highly suspicious. Further, 

 the suspicions raised by the structure and habits of the 

 cercaria were increased by the fact that its nurse-form was 

 the only one found upon the ground, although there was every 

 reason for expecting to find the larva of the liver-fluke, as an 

 infected sheep had been seen a few months earlier wandering 

 over the boggy spot from which the L. truncatulus was ob- 

 tained. I can testify that the sheep harboured numerous 

 flukes, for its liver was sent me for examination ; and there 

 could be no doubt that large quantities of fluke eggs had been 

 scattered all over the fields. My suspicions were accordingly 

 expressed in a report to the 'Royal Agricultural Society's 

 Journal' for April, 1881. 



During the summer of 1881 I was anxious to try infective 

 experiments with Limnseus truncatulus, but was unfortu- 

 nately unable to obtain any specimens; the localities near 

 Oxford, where I had formerly found it, were searched in vain. 

 I went out repeatedly in quest of this snail, having on several 

 occasions the skilled assistance of ray friend and colleague, 

 Mr. W. Hatchett Jackson, but we never found any other trace 

 of this species than the empty shells. It could not be dis- 

 covered in the localities given for it by Whiteaves in his 

 paper on the " Mollusca inhabiting the Neighbourhood of 

 Oxford."" My friends at a distance were appealed to, but were 



1 ' Arcbiv fiir Naturgeschicbte,' 1882, p. 80. 



2 'Proceedings of the Asbmoleau Society/ 1857. 



