122 



IXVEKTEBUATE ANIMALS. 



tary canal in many Mammals, birds, and lislics. Alioiit one hundred 

 and twenty species tif £r/niiorIii/ii<-/iii.i are known, liut it is doubtful 

 if any mature example has been fi)und in the human subject. 



Order II. CJordiacea. 



The Gonliaiya, or "Hair-worms," are eh.ngated, worm-like, or 

 hair-like Scolecids, in which the alimentary canal is without an 



.anus, and the sexes are in separate 

 individuals. 



The best known representative of 

 this group is the C(_immon Hair- 

 Wfirni (Oiinliiis aquatuniji, fig. 77) of 

 Euri>pe and North America. This 

 curious W(]rm is often found in 

 ponds and rivers, and may be two 

 or three feet long when mature. 

 (_)ther examples are found coiled up 

 I'ound the intestine of ground-beetles 

 or grasshoppers ; liut it is not clear 

 whether these are in a natural posi- 

 tion, so to speak, or whether they 

 may not be wandered individuals. 

 I IX such cases, however, the woi'm 

 ultimately leaves its insect-host, and 

 lietakes itself to water, where it lays 

 Idiig chains of wliite eggs. The em- 

 Ijryo is at first free and locomotive, 

 witli tliree pail's of cephalic hooks 

 (Hg. 77, P>), and a little protrusible 

 sudut. It passes its next stage en- 

 cysted in the Ia,rvie of water-insects, 

 into whieh it has bored its way, 

 and tlien it gains access to the bodies 

 of fislies which eat these larva', intimately, however, it becomes 

 free, and makes its way to land. 



Fig. 77. — OimliaccM. A, A siiiiiU ii 

 ili\idn;Ll ol' dvrdius aqutUlcus, < 

 tlic ii.'itural size. B, L<ai'va of '7o 

 dius stihfiiriatus, witli its pierciii 

 ^iroboscis and two rows of iiout; 

 enlarged. 



OrjiKii III. Nksiatoiiiea. 



The order Xi'iii(iiniil,;i iiK-ludrs the typical " Ivonnd-wiirms " and 

 " Thread-worms," some of wliich a,i(; ]),ai-asitic, while others lead a 

 ]M-r)iL;i,]]ently free existence. The bi.dy is cylindrical, the iutegu- 

 iiu'iit bring often ajioulited, liut ne\er lili.ited. TIlc nioutli is 

 ]>\:u:i-A ;uili'rioiIy ("Hg. 7»), and leads tlirough .a gullet ((/) to a strong 



