VERMES. 65 



Of the other Cestodc parasites we mention lure specially those 

 of Fishes, as the vulgar notion that the parasites of these 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. 43- 

 46). Here, again, we have a creature which infests two hosts. When 

 the larvae escape from the sheep they make their 

 way to a small pond-snail (Limnaa truncatula, 

 fig. 4."2) , into the lung-chamber of which they bore | 1 



their way. On leaving them the larva may be, 

 and is too frequently, eaten by a sheep, and makes Limna ' a truncatula. 

 its way into the liver of that animal, where it causes the disease 

 known as the "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 Piof. A. P. Thomas found as many as 7, 100,000 eggs in the 

 gall-bladder of a sheep which was suffering from rot, which, at that 

 time, had in its liver about 200 flukes. 



The simple non-parasitic 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 Thysanozoow. the general structure is 

 shown by a diagram in Case II., which is here reproduced (fig. 47). 

 Planaria, Thysanuzuun, and Bipalium serve to illustrate the forms 

 of members of this group. The simple Worms {Noncr tinea) with a 

 straight intestine, with a vent, and with a proboscis may attain to a 

 very considerable length ; Curinella and Lineus are represented by 

 large figures, and various species are shown in spirit. These forms 

 are, on the whole, very unsatisfactory to exhibit, on account of the 

 great difficulty of preserving them complete and uninjured. 



Nematodes (Thread-Worms or Round-Worms). — These are for 

 the most part parasitic, and infest plants as well as animals ; the 



