14 Experiments on the Development of the Liver-Jluhe. 
droppings, containing numerous eggs of the liver-fluke, was 
mixed with water, and the liquid poured over the turf, and 
the whole kept constantly moist. Into this, black and grey 
slugs were introduced. Subsequently the experiment was 
varied, eggs were obtained in large quantities from the livers of 
rotten sheep, and hatched out in a small volume of water, and 
the water, containing perhaps several hundred or thousand active 
embryos, poured over slugs confined in a small vessel. Every 
opportunity was given to the embryos of coming in contact 
with the slugs, and making their way into them. The embryos 
were watched under the microscope and seen swarming about 
the slugs, swimming around them, and occasionally stopping to 
bore, but one was never seen actually to penetrate the integu- 
ment of a slug. I had noticed slugs feeding at the road-side on 
the excrement of animals, and it occurred to me that the embryo 
or egg might possibly be swallowed by the slug, and afterwards 
bore its way through the walls of the intestine into the body- 
cavity. Accordingly, eggs containing nearly mature embryos 
were strewn on cabbage-leaves and given to slugs. One of these 
dissected showed that the eggs escape the crushing action of the 
radula and jaw of the slug, for only one egg was in any way 
injured. 
In dissecting specimens of the black slug, numbers of the 
cystic form of Tcenia arionis were found, always close to the 
respiratory cavity, and accordingly other embryos and eggs of 
the fluke were injected into the pulmonary chamber of the 
slug. 
The slugs experimented upon were Arion ater (more than 
fifty individuals), Arion hortensis, Limax agrestis, and Limax 
cinereus. These were dissected subsequently at different periods 
after infection, but in no case, with one exception, was any 
larval Trematode found. This exception was that of a black 
slug belonging to those first infected. It contained sporocysts 
belonging to Cercaria limacis, Moulinie (= Cercaria trigono- 
cerca, Diesing). These sporocysts include cercariae provided 
with boring-spine and only a rudimentary tail, and as the sporo- 
cysts are left behind in the mucous trail of the slug, Moulinie * 
conjectured that the cercaria of the liver-fluke might occur in 
some such form. 
The sporocysts, as found on the surface of the slug or the 
track of mucus it leaves in crawling, are oval or cylindrical sacs 
0'8 mm. long, with one extremity produced into a sort of neck. 
In the centre of this is a slight depression, and the whole acts as 
a rudimentary sucker. The surface is formed by a thin trans- 
* ' Memoircs de I'lnstitut Genevois,' vol. iii. p. 2G7. 
