1 46 ENTOZOA. PAET in. 



form. The eggs of the Tsenia may be introduced into 

 the human or animal stomach ; for dogs and other car- 

 nivora which eat raw unwholesome meat are infested 

 by full grown tsenia, which fix themselves to their 

 entrails by their hooks and suckers, while at the same 

 time egg-bearing segments separate successively from 

 their posterior extremity, and being voided scatter the 

 eggs far and wide on land and in water. 



The young of some Entozoa undergo various trans- 

 formations, as those of the Distoma of the Lymnsea. 

 When full grown that entozoon is like a sole, flat, 

 broad, and long, with a kind of head at the broad end, 

 and two suckers on its under-surface, in one of which 

 there is a pore serving as a mouth, whence an alimen- 

 tary canal extends, which spreads in branches almost 

 throughout the whole body. This animal has a fila- 

 mentary nerve round its gullet, from which minute 

 fibres pass to the mouth, and two filaments extend 

 backward on each side as far as the second sucker. 

 The eggs which occupy the whole margin of the body 

 are developed into worms, each of which seems to be 

 merely a mass of structureless cells enclosed in a con- 

 tractile case. By a second change each of these cells 

 is transformed into a freely swimming ciliated zooid 

 endowed with eyes. Having escaped from their con- 

 tractile case, they remain for a time in that state, and 

 then imbed themselves in the mucus on the foot of the 

 fresh- water mollusk Lymnsea, or pond snail, where they 

 are transformed into true Distomata, and ultimately 

 enter into the body of the Lymnsea itself, where they 

 lose their eyes and cilia, which are no longer of use in 

 their dark and permanent abode. The Fluke found in 

 the livers of sheep that have the rot is a Distoma. 



The Nematoid order, or thread-worms, that live in the 

 muscles of men and animals, are long, smooth, and cy- 

 lindrical, with a structureless skin covering layers of 



