42 ENTOZOA FOUND IN MAN. 



superiorly, and the others laterally and inferiorly; 

 the valves, between which the mouth is situated, are 

 marked on their internal surface with minute inden- 

 tations. 



The male is smaller than the female ; its tail is 

 bent or twisted, and is sometimes provided with two 

 lateral membraneous wings, or with two rows of 

 papillae, or more rarely with a sucker. 



The genus Ascaris comprises many species which 

 are found in the intestines of vertebrated animals. 



The species wliich is often observed in the human 

 subject is the Ascaris Lumbricoides. It varies from 

 a few inches to a foot in length, and is very similar 

 in appearance to the common earth-worm, for which 

 it was formerly mistaken. The head of this entozoon 

 is not armed with hooks, and the mouth is small, 



Fig. 9.^ 



and furnished with three valves, which are minutely 

 denticulated upon their mner surface ; the body is 

 diminished in size towards either extremity, and it 

 is striated transversely. 



The ova of the Ascaris lumbricoides are not de- 

 veloped m the intestines, but are always expelled 

 with the evacuations. Their development occupies 

 a long period, and they pass through the autumn 

 and the winter without any change taking place in 

 them ; sometimes they may continue for even a year 



^ The Ascaris lumbricoides ; the worm in the figure is reduced 

 to about one-third of the usual size. 



