" GROUSE DISEASE " STRONGYLOSIS 



225 



accommodated within the shell (Fig. 23). The alimentary 

 canal meanwhile has gradually been developing, so that by 

 the time the embyro 

 attains a cylindrical 

 form the canal is 

 found to extend 

 throughout the body 

 as a distinct cell- 

 walled tube (Figs. 

 24, 25). During T the 

 whole of this period 

 the embryo remains 

 quiescent, but about 

 an hour or so before FlG - 21 - FIG. 22. 



it leaves the egg-shell Developing ova of T. pergracili*. 



it commences to exhibit a certain amount of movement. This 

 movement gradually increases in extent and vigour, until it 

 ultimately overtaxes the resistance of the egg shell, which 



FIG. 23. FIG. 24. 



Formation of the larva of T. pergracilis. 



TlG. 25. 



suddenly ruptures. The success or failure of these efforts on 

 the part of the young worm appears to depend on the amount 

 of water which is imbibed from the outside, for if only such an 

 amount of water be added to the culture as is absolutely necessary 



