90 



NEMATHELMINTHES 



Nervous System. — A nerve ring encircles the esophagus con- 

 nected to two large nerve cords, one ventral and one dorsal; with 

 several other lesser cords and numerous nerve strands and connec- 

 tives.^ 



Other Ascarids. — Parascaris equorum, the largest species of 

 Ascaridae, is found in the horse family where it infests the small 

 intestine. Males are eight to ten inches and females ten to twelve 

 inches long. This species was used by Van Beneden in his classical 

 study of chromosomes. It is said that one-third of the dry sub- 

 stance of A. megalocephala consists of glycogen. 



Ascaris vitulorum infests calves, attacking the small intestine 

 and sometimes ascending to the abomasum. It produces diarrhea, 

 colic and intestinal inflammation. Ascaris ovis infests the small 

 intestine of sheep. Ascaris suilla {lumbricoides) infests the hog's 

 small intestine. If it enters the stomach it causes nausea; if it 

 infests the pancreas it may occlude the bile ducts and cause jaundice. 

 Infesting the lungs, it causes " thumps." Toxocara canis and 

 Toxuscaris leonina infest dogs; Toxocara mystax infests cats. As- 

 caridia lineata occurs in poultry, infesting the intestine. Ascaridia 

 maculosa (syn. Heterakis maculosa) attacks pigeons. 



Enterobius (Oxyuris) vermicularis (Oxyuroidea), a white worm 

 called the pinworm of man, is less than J/2 inch long. The male is 

 2 mm. to 3 mm., the female 9 mm. to 10 mm. in length. The color 

 is white, the body is expanded anteriorly. Metchnikoff believed 

 the pinworm an important cause of appendicitis. Several con- 

 flicting reports have since appeared, but there is good evidence that 

 the eggs and larvae of the pinworm are found in diseased appendices. 

 Oxyuris eqiii^ the horse pinworm, is found in the rectum and large 

 intestine of the horse, ass and mule. 



Rhabditis nigrovenosa {Rhabdiasoidea). — In this form we find 

 well marked the alternation of generations — hermaphroditic with 

 sexual. It is found in the lungs of the frog and toad in a her- 

 maphroditic condition. The eggs are laid and pass into the ali- 

 mentary canal from the lung. They develop in water or soil into a 

 nematode in which the sexes are separate. Fertilized eggs develop 

 internally and eat all but the cuticle of the mother. From a free 

 life in the mud they pass into the frog's lung, by way of its cuticle 

 and mouth. 



1 For nervous system of Ascaris see Handbuch der Zoologie, v. 2, Achte Lieferung 

 Teil (4) Bogen 23-32, ss. 280-283. 



