30 



The life history of Syngamus trachealis is as follows: Earth- 

 worms containing the embryos are eaten by the fowl. The 

 embryos are liberated from the intestine of the earthworm and 

 work their way through the esophagus into the lungs and bronchi. 

 Here they pass through the nymph stage and acquire sexual 

 maturity. The male and female then unite, work their way into 

 the trachea, and attach themselves to its mucous membrane by 

 their sucker-like mouths. Between six and seven days are re- 

 quired from its entrance into the fowl until its attachment to the 

 trachea. In about seven days more the eggs within the body of 

 the worm become mature. They are coughed up into the mouth, 

 swallowed by the fowl, and pass through it into the soil. In about 

 three weeks, the time varying somewhat according to the tem- 

 perature, these eggs, exposed to the moisture and sun, hatch ; the 

 embryos are taken in their food by the earthworm, where they 

 remain until picked up by some bird, when the above process is 

 repeated. Some years one-half or two-thirds of the young fowls 

 in certain localities are destroyed by this disease. This investiga- 

 tion proves that if they were kept from eating infested earth- 

 worms, that terrible scourge of poultry, the gapes, would be en- 

 tirely prevented. Not only this, but it serves as a key to unlock 

 the mysteries surrounding several other diseases, caused by para- 

 sites belonging to this family; namely, the lung worm of calves 

 (Strongylus micrariis), the lung worm of hogs (Strongylus cb'iga- 

 tus), the lung worm of sheep (Strongylus filiaria), the grouse 

 disease (Strongylus pcrgracilis). Great numbers of calves, hogs, 

 sheep and grouse are yearly destroyed by these parasites. Their 

 intermediate hosts have never been discovered. From certain 

 inquiries which I have made, I venture to predict that the earth- 

 worm will be found to be their intermediate host.* 



*Cobbold in hi? work on " Parasites," page 336-346, after a series of observations states 

 his belief that the earthworm may act as an intermediate host for Strongylus micrurw. 



