98 NEMATHELMINTHES 



As an outgrowth of this pioneer work on alkyl-resorcinol deri- 

 vatives, Doctor Leonard of Johns Hopkins University has developed 

 the internal antiseptic "hexyl resorcinol." 



Thyynol in 6o-grain doses is effective in the treatment of human 

 helminthiasis. The active principle of oil of chenopodium, called 

 ascM-idole, is used in doses of 0.5 c.c. Calomel, santonin, and oil 

 of male fern {Aspidiuni) are beneficial in trichinosis, but not effective 

 after the parasites have become encysted. 



Nematodes as Laboratory Material. — Certain free-living aquatic 

 nemas are so resistant to external conditions that they can be shipped 

 alive long distances, and are thus favorable laboratory material for 

 zoological courses in schools and colleges. Prominent among these 

 are species inhabiting foul mud, such as Metoncholaimus pristiurus 

 (marine) and its close relatives, and certain species of Dorylaimus 

 (fresh water). M. pristiurus have been shipped thousands of miles 

 both summer and winter, and used successfully.^ 



General Consideration of the Nemathelminthes 



Distribution. — Nematodes are found from the depths of the sea 

 to the tops of mountains and in hot springs and Antarctic ice. 

 While it was formerly supposed that they were almost all parasitic, 

 it is now known that besides infesting animals and plants of all 

 species, there are very many, small, free-living species. 



Physiology. — Nematodes usually have a simple digestive tract, 

 well-developed excretory organs, tubular gonads and a nerve ring 

 with sensory papillae and both dorsal and ventral nerves. 



Fossil Relatives. — The Nematodes range from the upper Paleo- 

 zoic to the present. They are found in the Coal measures and 

 parasitic in insects in the Tertiary amber. 



Ancestry and Relationships to Other Phyla. — The various classes 

 of Nemathelminthes differ and it is still very doubtful whether they 

 should be grouped into a single Phylum. Some of the families 

 formerly classed under the Nemathelminthes are now separated, 

 apparently resembling the Annelida. 



References on Nematodes 



Chandler, A. C. 1922. Animal Parasites and Human Diseases. J. 

 Wiley and Sons, N. Y, 



* Cobb, N. A. 1 93 1. Science, vol. 74, pages 489-490. 



