FLATWORMS, KoUNDWnRMS, AND ROTIFERS 73 



Varied situations, and on water and land show this. Recall 

 that the rotifers lay two kinds of eggs to meet different- 

 conditions and maintain an existence. 



Progression. — It is evident tiiat the animals discussed 

 in these four bi'anches are more highly developed tluiu those 

 of the foregoing branch. Starting with the flat\\'<.)rms, we 

 hnd that many of them have a rather complete digestive 

 system and concentrated nervous system. The digesti^'e 

 system of the flukeworm consists of a moutli, pharynx, gul- 

 let, and intestine, while the nerv(jus system consists of a 

 ring of nerve matter ai'ound the gullet which gives off a 

 nmnber of nerves, one i)air i-unning the lengtli of the Vxjdy. 

 Trichinella has a mouth, phai'vnx, and intestine, with a. ring 

 of nerve matter about the pharynx that gi\'es off' nei'\'cs. 

 The rotifers ]30s.sess a mouth, pharA'ux, gullet, stcjmach, and 

 intestine, — the most complete dig(>stive system that we 

 have seen so far. They also have a small brain. 



CLASSIFICATION OF THE EXAMPLES 



Branch IV — Platyhcliniuthes. 

 Class — Trcmatoda. 



Order — Din;('iietifa. 

 Type of Oi'dcr. 



Disloiiiiiiii hcpaticum — Liver flukeworm. 

 Class — Cestoda. 



Order — Polyzoa. 

 Types of Order. 



Tail id sal ill III — Pr)i-k ia|ioworm. 

 Taenia sai/innta — Beef tapcworm. 

 Br.\ncii V — Xematholmiiitlies. 

 Class — Xematoda. 



Order — Nematoid^a. 

 Type of Oi-ilcr. 



TriddiiiUa spiralis — Ti'iehina 



