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118 STARFISH GALLERY. 
animals are dangerous to man has been shown to be entirely 
erroneous. 
The Flukes infest animals of all kinds ; that which is most 
dangerous to sheep, and the cause of much pecuniary loss (Distoma 
hepaticum), is selected here as a type ; its structure is shown by a 
large model, and its life-history by a series of diagrams (Figs. 10-13). 
Here, again, we have a creature which infests two hosts. If the 
larvse which escape from the sheep fall on wet 
Fig. 9. ground in or near a pool, they make their way 
to a small pond-snail {Limnoza truncatula, Fig. 9), 
into the lung-chamber of which they bore their 
Limnxa Truncatula. way. On leaving them the larva may be, and 
is, too frequently, eaten by a sheep, and makes 
its way into the liver of that animal, where it causes the disease 
known as the " liver rot." 
The damage done by the liver-fluke may be imagined from the 
fact that in the winter of 1879-80 no less than three millions of 
sheep died of rot in the United Kingdom ; this heavy loss is no 
doubt largely due to the immense number of eggs to which a single 
fluke may give rise. It has been estimated that every fluke may 
produce, during its life, several thousands of eggs ; and in one case 
Prof. A. P. Thomas found as many as 7,400,000 eggs in the gall- 
bladder of a sheep which was suffering from rot, and which, at that 
time, had in its liver about 200 flukes. 
The non-parasitic Flat-worms are shown, magnified, in the upper 
parts of Cases I. & II. The Turbellaria proper, without any or 
with a simple or a branched intestine, but without a vent, are 
represented by Convoluta and Thysanozoon : the general structure is 
shown by a diagram in Case II., which is here reproduced (Fig. 14). 
Planaria, Thysanozoon, and Bipalium serve to illustrate the forms 
of members of this group. 
The Nemertine Worms {Nemertined), with a straight intestine, 
with a vent, and with a proboscis, may attain to a very considerable 
length ; Carinella and Linens are represented by large figures, and 
various species are shown in spirit. These forms, which used to be 
very unsatisfactory to exhibit, on account of the great difficulty of 
preserving them complete and uninjured, are now, with improved 
methods, very satisfactorily shown, as the specimens purchased from 
the Marine Biological Laboratory at Plymouth prove. 
Nematodes (Thread-Worms or Round- Worms). — These are for 
