Experiments on the Development of the Liver-Jiuke. 19 
that the sheep drank. Its waters were searched for molluscs, 
but none found except a single minute specimen of Cyclas and 
two equally minute specimens oi Phi/sa fontinalis. It contained 
also a few aquatic larvae — which, however, were free from Tre- 
matodes — but the only abundant form of animal life was Gam- 
marus pulcx. Some of these Gammari contained thin-walled 
oval cysts, including immature distomes which have been de- 
scribed but not named by De la Valette.* The surface of this 
distome is marked with fine granules, as is probably that of 
Fasciola from the earliest period, but the oral sucker is consider- 
ably larger than the ventral, and some other points in its anatomy 
are against the view of its being the larval form of the liver-fluke. 
Limax aqrestis was fairly abundant in the fields, and Avion ater 
occurred in smaller numbers, more especially on the margin of the 
wood, but the dissection of a score of each species and microscopic 
examination of all their tissues did not reveal a single larval 
Trematode. No water-snails could be discovered in any of the 
other ditches, and the only other animals found on these fields, 
which need be mentioned here, inhabited one of the wet places 
referred to above. Here two or three small specimens of Lim- 
nccus truncatulus and some aquatic larvae were found. These 
contained no cercariae, but in another L. truncatulus found at 
the same spot a month later, an interesting form of cercaria 
occurred. It has certain points of resemblance with both Cer- 
caria agilis and Cercaria tuberculata of De Filippi,| but appears 
to be a new species. It is produced in a cylindrical redia, 
1'3 mm. long, with two short conical processes at the posterior 
end. The young rediae have in addition two similar but smaller 
processes near the anterior extremity, and there is an opening 
which gives exit to the cercariae just in front of one of them. 
The digestive tract is well marked, but short and of a clear 
yellow colour ; its length is almost constant in the rediae of 
different ages, and is 0*22 mm. The pharynx is distinct. The 
mature redia contains one, two, or three cercariae, and germs of 
others. The free cercaria has a body of oval form, about 0 * 3 mm. 
long, but is of very changeable shape ; the tail is more than twice 
as long as the body. The oral sucker is subterminal and 
0 • 06 mm. in diameter ; the pharynx is distinct and 0 ' 034 mm. in 
diameter ; the ventral sucker is central, about the same size as 
the oral, or but little larger. Digestive tract simple and forked. 
There is no head spine, and the anterior part of the body is 
covered with exceedingly minute spines. On each side of the 
middle line, extending the whole length of the body, is a white 
* ' Verhandlungen des naturforscli. Vereins d. preuss. Rheinlande,' 1859, p. 56. 
t " Memorie della Reale Accademia delle Scienze di Torino." Serie II. vol. 
xviii. p. 206. 
c 2 
