ROUN DWORMS— THE NEMATHELMINTHES 167 



This same principle holds true for the parasites of the blood stream 

 and other parts of the body. There are physiological differences in the 

 blood and other body fluids that make it difficult for parasites to be adapted 

 to different species of animals. The larvae of the dog hookworm some- 

 times enter the human skin. In the unnatural surroundings, however, 

 they do not find their way to the lungs and thence back to the intestine as 

 they would in the dog. Instead they wander around under the skin, 

 creeping along. Such an infection is known as "creeping eruption." 

 They eventually die or their death can be hastened by freezing them with 

 a spray of ethyl chloride. 



Classification and Derivation of Scientific Words 



Phylum Nemathelminthes (Gr. nema, thread; helmins, worm; refers to the 

 thread-like nature of many of the roundworms). 

 Genus A. Ascaris (Gr. ascaris, an intestinal worm). 



species 1. lumbricoides (L. lumbricus, earthworm; refers to the 

 resemblance of this species to earthworms). 

 Genus B. Necator (Gr. necator, killer; this small hookworm fre- 

 quently is a killer), 

 species 1. americanus (Eng. American; refers to location). 

 Genus C. Trichinella (Gr. trichos, hair; refers to the hairlike appear- 

 ance of this worm). 

 species 1. spiralis (Gr. spiralia, a coil; refers to its coiled condi- 

 tion as a larva in muscle). 

 Genus D. Wucheria (From Dr. O. W. Wucherer). 



species 1. bancrofti (named from man, Bancroft, who did pioneer 

 work with the filaria worm). 

 Genus E. Enterobius (Gr. enter on, intestine; bios, life; spends its life 

 in an intestine), 

 species 1. vermicularis (L. vermiculus, a little worm). 

 Genus F. Gordius (L. gordius, a knot; these hair worms may some- 

 times be found tangled in knots). 



REVIEW QUESTIONS 



1. How is ascaris able to exist in the absence of oxygen in the intestine? 



2. Why are digestive glands unnecessary on the intestinal tract of ascaris? 



3. Why is the extensive branching of the digestive and excretory systems, such 

 as was found in planaria, not necessary in ascaris ? 



4. Why is it necessary for the female ascaris to lay such a large number of 



eggs? 



5. Trace the journey of the ascaris larva through the body. 



6. How do the feeding habits of the hookworm differ from ascaris? 



7. Trace the life cycle of the hookworm. 



