The Rot in Sheep. 
117 
bore their way into w.iter-snails, to cast off tlicir tails, and 
dcvelope into Jliihcs with perfoc t sexual organs — thus completing 
the series of changes. After entering the body of the snail, 
and before being transformed into the fluke, the ccrcaria rolls 
itself into a little ball and passes into the j^upa state, Ijy emitting 
from the surface of its body a mucous secretion which hardens 
and encloses it. This change was first observed by Nitzsch, and 
afterwards by Siebold and others. The annexed engraving 
( ////. 13) represents t\\c pupa state of the Ccrcaria ephenwa. The 
letters point — rt, to the oral sucker, and c, d, to the urinary 
organ. 
Fig. 13. 
Encysted Ccrcaria ephemera. After Huxley. 
Encysted cercaria?, besides adhering in large numbers to a 
great variety of mollusca, the larvce of aquatic insects, &c., are 
likewise found free in water. How long their jnipa state may 
continue is not known, but, according to the experience of Steen- 
strup, in some varieties of cercaria it does so "for many months." 
Thus it has been proved that the piqm state of the cercaria is 
the penultimate form of the fluke, and it is probable that in 
this state the entozoon enters the orffanism of vertebrate animals 
as well as others. Kiichenmeistcr states that " when De la 
\ alette set about administering the tailed, free living forms — 
that is to say, the cercaria; — the result of a metamorphosis of 
these forms into mature distomata did not occur. He then 
directed his attention to the forms originating from the cercarice 
just referred to, which are enclosed in cysts, and, although still 
asexual, are already in other respects somewhat further deve- 
loped .... When administered in this state the young disto- 
mata are quickly provided with germ stock, testes, and ovaries. 
According to De la Valette's experiments, it is certain 
that the Ccrcaria echinifera is converted very rapidly in the 
intestine of warm-blooded animals, and slowly in cold-blooded 
species, into Disioma echinifera, Val. ; that Cercaria Jiava of the 
ephemera becomes transformed into Monostomum Jiavum of the 
finches and sparrows ; and that Cercaria echinata is converted 
into Distoma echinata Anatis Boschadis (Zeder)." 
Although the transformation of enci/sted cercarice into distomata 
