CH. IX] OF DOMESTIC ANIMALS 321 



by Ehlers that if eggs containing embryos are swallowed 

 by birds, mature individuals are found in the trachea 

 within a fortnight. Walker has further proved that the 

 embryos remain alive within the alimentary canal of 

 earthworms, and that birds which eat such worms in a 

 short time suffer from " gapes." Pigeons and poultry also 

 suffer from the attacks of Heterakis maculosa (Ascaris 

 columbce) and H. papillosa. These worms swarm in the 

 intestines of the birds and may cause death. Both are of 

 small size ; the former from 16 to 34 mm., the latter from 

 7 to 15 mm. in length. The eggs develop in moisture, 

 and the larvae reach maturity in about three weeks. No 

 intermediate host is required, the parasites entering the 

 birds with the food. 



A large number of plants are injuriously affected by 

 these worms. " Clover-sickness," " beet-sickness," " ear- 

 cockles " in wheat, and frequent diseases of the roots 

 of tomatoes, cucumbers, cabbages and other plants are 

 all directly due to these "eel-worms." Indeed there is 

 hardly any plant that may be regarded as entirely immune 

 from their ravages. The small species often found in stale 

 paste and in vinegar, and known as "paste-worms" and 

 " vinegar-eels," are members of this successful order of 

 parasites. 



As a group they are most difficult to combat, since 

 most can withstand prolonged drying, even for years, with 

 unimpaired vitality. 



L. 21 



