condition for many years, but become active and sexually mature 

 when liberated in the digestive tract of a new host. 



The guinea worm, Dracuncidus medinensis, is a remarkable 

 tissue parasite occurring in warm countries, especially Arabia to 

 Hindustan. The male, an organism of about 20 mm. in length, is 

 seldom found. The female is a very slender thread-like organism 

 of 50 to 80 cm. It is found associated with ulcerated patches on 

 the body surface. This is the stage of discharging the young and 

 takes place about a year after the primary infection. The ulcers 

 are commonly found about the feet or ankles, the centre in each 

 case being occupied by a projecting portion of the worm. The 

 native method of extracting the worm is to catch the end between 

 the edges of a split stick, exercising a slight pull by rolling the 

 stick around. The process is continued for several days. If the 

 worm is broken, however, the direct spread of the larvae may 

 greatly increase the infection. Normally the larvae live in the 

 water and pass through a crustacean host {Cyclops). They gain 

 access to the human body through the ingestion of Cyclops with 

 drinking water. 



The filariae are somewhat similar forms which are widely dis- 

 tributed through various vertebrate hosts, occurring for the most 

 part in the blood and lymph. Filaria bancrofti (F. sanguinis 

 hominis) is a human parasite of the lymphatic glands and other 

 organs, generally distributed through the warmer zones. The 

 female is about 50 mm. in length, the male being scarcely half as 

 long. The larvae are most common in the capillaries of the lungs, 

 and usually appear in the surface capillaries at night, or when the 

 patient sleeps. Infection takes place through species of mosquitos, 

 the latter playing the role of secondary hosts. 



Acanthocephala, "thorn-headed worms", include a small 

 number of species in which the anterior end of the body is narrowed 

 and rounded, and possesses an armature of curved hooks. The 

 chief species is Macracantharhynchus hirudinaceus , of which the 

 male is 10 to 15 cm., the female 30 to 50 cm. in length. It is found 

 usually in the intestine of the pig but may occur in other mammals 

 and in man. 



Gordiacea, "hair worms", are fairly common as adults in 

 fresh water, whiFe their larvae are parasitic in insects or molluscs. 

 Occasionally they occur in the human intestine. The common 

 field cricket is often parasitized by the larvae of Paragordius varius. 



ANNULATA. 



Two characteristic invertebrate phyla, the Annulata and 

 Arthropoda, are readily distinguishable from all others by the 



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