228 THE GROUSE IN HEALTH AND IN DISEASE 



oesophageal bulb (Fig. 29) become resolved into a simple thin 

 cuticular covering (Figs. 30, 31). The walls of the intestine, 

 which have gradually increased in size, become more clearly 

 defined, and now appear as cylindrical turgid cells distended 

 with large globules of highly refractile substance, giving the 



i\ 



FIG. 28. FIG. 29. FIG. 30. FIG. 31. 



Changes in T. pergracilis during ecdysis and encystment. 



larva a characteristic appearance by which it can be readily 

 distinguished from free-living nematodes (Fig. 30). 



The whole body appears to have slightly narrowed during 

 the process of metamorphosis, by the conclusion of which the 

 larva has become changed into a slender actively moving worm, 

 with a simple elongated oesophagus without mouth capsule 

 (Figs. 30, 31). Accompanying the metamorphosis in structure 

 is a marked change in habits, for instead of burrowing into the 



