Class 2. Trematoda. Order 2. Distomew. 



149 



Birds, as also in tliat of various Marsh -birds which devovir the whole Snail, the 

 young Trematodes contained in the " rods" undergo their complete development, 

 and become the normal hermaphrodite generation, which has been desonbed 

 under the name Distomv/m macrostomum. 



Pig. 105. 



Pig. 106. 



Pig. 105. PoVystomum integerrvmum, from the central side, m Month, » sncker, 

 t gnt. — After Zeller. 



Pig. 106. A Snail, with Leuchochloridium paradoxum in hoth tentacles. B the same, 

 taken out of the SnaiL C Distomnm macrostomnm. p penis, Sj fore-, Sn hind-sncker, t gnt. 

 A and B natural size, C X 20. — After Zeller. 



Class 3. Cestoda (Tapeworms). 



The Cestoda differ from the Trematodaj with, which they are 

 nearly related, ui that they have no digestive tract, and almost 

 always form chains by budding. 



A cestode chain consists, at first, of an asexual individual, the so- 

 called "head" (scolex), which is provided at the anterior end wtth 



Pig. 107. Tasnia mediocanellata, part of the chain, natural size. — After Leuckart. 



suckers, hooks, or other organs of adhesion. Behind the head follows 

 a larger or smaller number of segments (proglottides), i.e., sexual 

 individuals of different developmental grades, and of different sizes. 



