20 



BULLETIISr 817, U. S. DEPT. OF AGEieiTLTXJBE. 



with which young chickens can readily be infected by feeding the 

 eggs of gapeworms taken from turkeys. In turkeys full-grown 

 gapeworms commonly reach a length of 25 to 40 mm., but in chickens 

 infected with material from turkeys the egg-producing adult rarely 

 exceeds 15 to 20 mm. in length. 



Fig. 4. — Ascaris suum. Larva in liver of mouse 10 days after infection. Photomicrograph 

 of living specimen. Magnified. 



In the case of migrating Ascaris larvae differences of size are no- 

 ticeable in different species of host animals, if a comparison is made 

 of larvse taken from different animals at corresponding times fol- 

 lowing infection. The following table has been compiled from the 

 results of experiments on mice, guinea pigs, and rabbits : 



