88 American Quarterly Microscopical Journal. »- 



been discovered in the lion or tiger, and only two in the cat: 

 one for the domesticated, and one for the wild state. They 

 exist quite abundantly in bats, reptiles, and fishes, and display 

 great partiality for frogs and toads. 



The order is easily classified, as follows : 



Monostomidse, Family I. 



Distomidae, " II. 



Trematoda \ Tristomidse, " III. 



I Polystomidae, " IV. 



l^ Gyrodactylidae, " V. 



The first three families are so named because they have re- 

 spectively one, two, and three suckers ; or, as was formerly 

 supposed, " perforated mouths." 



In the fourth family a particular number of suckers need 

 not be insisted on, while the fifth family are characterized by 

 having peculiar hooks around the posterior disk. 



Plate IX., Fig. I, represents a distome from the bladder of a 

 frog. This animal, visible to the naked eye, can be readily 

 obtained, and but few frogs will be sacrificed in vain. 



The first thing noticed is its smooth integument, composed 

 of muscular substances, always of the non-striated or smooth 

 variety. 



At the anterior extremity is the anterior or cephalic sucker 

 {A), perforated at the bottom (C), which represents the oral 

 cavity. A little posterior to this is a larger sucker called the 

 posterior sucker, or acetabulum {B). This is not perforated, 

 being used as an organ of locomotion, or as an anchor. 



The oral cavity (C) enlarges to form the pharynx {D), to be 

 continued into the oesophagus (^), which divides into two 

 long blind tubes {F) extending nearly the whole length of 

 the body. At G are seen little granular masses, doubtless 

 food. 



In order to study our distome in its native element, it was 

 examined while resting on the exposed inner surface of the 

 bladder of the frog. While thus situated, a blood-corpuscle 

 {H) was seen to pass into the oral cavity, and by watching 

 its course, the blind stomachs were traced quite satisfactorily. 

 When the body was active, it would be driven toward the 

 blind end of these tubes ; but as soon as motion ceased, and 

 the body was comparatively quiet, then the corpuscle would 

 invariably be driven to the pharynx and there remain till 



