Development of the Liver-Fluhe. 
451 
on the other hand many of the organs of the adult are not 
visible in the voun<r, even in rudiment. The most valuable of 
the permanent characteristics are the relative proportions of the 
suckers and the nature of the cuticular structures. It is usually 
considered that the suckers preserve the same relative propor- 
tions during growth ; but such is not the case in Fasciola hepaticUy 
for here the ventral sucker grows relatively more rapidly than 
the oral. This is perhaps only natural, as the hinder portion 
of the body rapidly outstrips the anterior portion during growth, 
as it contains the reproductive organs. This fact is of greater 
importance, seeing that we have so few characteristics to assist 
us in the difficult task of connecting the larva with the adult. 
In the adult, the diameters of the oral and ventral suckers are on 
the average in the ratio 1 : 1'35, though there is much individual 
variety. In the largest fluke I possess, 34 mm. in length, the- 
ratio is 1 : 1"42. But in the smallest specimen I have yet foundy 
Avhich was only I'l mm. in length, the two suckers are of exactly 
equal size, and the same is the case in a specimen 2*2 mm. in 
length. Examples of the size of the latter, however, have 
usually the ventral sucker rather larger, the ratio of the oral to 
ventral sucker being: on the averag-e about 1 : I'l. In still larger 
examples, 6-8 mm. long, the ratio is about 1 : 1'2. It may be 
inferred, therefore, that the suckers in the larval form of the 
liver-fluke scarcely differ in diameter, though the ventral mav 
possibly be the larger to a trifling extent. In the tail-less larval 
form found by Leuckart, the ratio of the suckers was as 7 : 8 or 
1: 1-143. 
It is worthy of mention in this connection that no less than 
ten species of rediae or sporocysts have been recorded containing 
tail-less distome-larvae instead of the more usual tailed cercariae. 
jNIost of the species appear to be good, though others are verv 
imperfectly known. De Filippi described under the name of 
Distoma paludinge impurce inerme, a tail-less distome-larva, 
which has many points of resemblance with the one found by 
Leuckart, and was produced in a similar redia without any 
lateral processes, and he proved that it was the larval form of 
Distoma perlatiirn, found in the tench, &c. From these observa- 
tions of De Filippi it seems probable that the tail-less form, 
found by Leuckart is destined to develop in a cold-blood host 
rather than in a mammal. 
Another of the rediae found in Limnccus truncatulus appears 
to be the same as the one I had already met with in the same 
snail on infected fields at Wytham.* The cercariae produced 
with it are characterised by the presence of a lobed lateral organ. 
* 'Eoval Agricultural Society's Journal,' vol. xvii., 1881, p. 19. 
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