VERMES 



IO9 



suckers arc always present by means of which 

 they may attach themselves to the host. It 

 is the presence of these suckers which has 

 furnished the name of the class, and we find 

 them, as we should expect, much more numer- 

 ous in the ectoparasitic species than in the 

 entoparasitic, for the former require a much 

 firmer attachment than the latter. The ento- 

 parasites always have one sucker which sur- 

 rounds the mouth at the anterior end of the 

 body, and this may be the only sucker present ; 

 but generally there is a second farther back 

 on the mid-ventral line (Fig. 100). In the 

 ectoparasites there is often a sucker on each 

 side of the mouth and several others at the 

 posterior end of the body. Many of the Trem- 

 atoda a v re parasitic on the skin or the gills of 

 fishes and other aquatic animals, and many 

 others are found within the bodies of the 

 higher animals, in various parts of the ali- 

 mentary canal, in the blood system and the 



excretory system. 



J J Fig. 99. Ml > ■ mum 



Some of the entoparasites in process of budding, 

 produce serious diseases in their c ' c '' clliated - 1 



e, eye-spot; i, intes- 



hosts. A number occur in man, tine; m, »t\ m", m'", 

 more particularly in the tropics, ™™£- J r f '^X" 

 while the most troublesome of and Hasweii's Text- 

 all are probably the flukes, es- 

 pecially the liver fluke of the sheep, Distomum 

 kepaticum (Figs. 100 and 100 bis), which in Eng- 

 land alone has caused the death of millions of 

 sheep. A similar species, somewhat larger, is 

 found in the liver of the red deer in America. 

 ven " The iiver fluke of the sheep is oval or leaf-shaped 



tral aspect, excr, 



excretory pore; and attains a length of from two to three centi- 

 mo, m<»uth; repr, meters while the fluke of the deer may be as 



reproductive aper- J 



ture; sckr, poste- much as ten centimeters long. The mouth is at 

 nor sucker (After tn anterior end of the body, surrounded by a 



Parker and Has- J ■ 



well.) sucker, and a short distance posterior to it on 



excr 



Fig. ioo. Disto- 

 mum hepatic urn ; 



