226 THE GROUSE IN HEALTH AND IN DISEASE 



to set the process of development in motion, and the culture 

 be then allowed to dry somewhat, it will be found that the 

 embryo is incapable of rupturing the egg shell. A slight collapse 

 of the egg shell, owing to an insufficiency of water, causes the 

 death of the embryo at any period of its growth. Hatching 

 usually takes place from thirty-six to forty-eight hours after 

 the egg passes out of the bird ; but in summer it may be delayed 

 for even as long as a month. 



When the embryo is hatched there seems little purpose in 

 its early movements. The cuticle, at first irregularly crinkled, 

 gradually smoothens as the parasite becomes saturated with 

 water. The movements now appear to gain in purpose, and 

 very soon the little worm is actively moving about, obviously 

 in search of food. 



When newly hatched, the embryo measures 0'36 mm. in 

 length, and 0*15 mm. in greatest thickness (Figs. 26, 27). The 

 body is cylindrical, tapering to a slender pointed tail in the last 

 O'l of a mm. of its length. Anteriorly it maintains an almost 

 uniform diameter to within 0'05 of the mouth, when it shows 

 a slight and gradual narrowing. The anterior extremity ends 

 bluntly, and has a diameter of 0*0075 mm., presenting at its 

 summit the small rounded opening of the mouth capsule. At 

 0*06 mm. from the tail the anal pore opens with but little 

 external indication. 



Alimentary Canal. Two faint parallel lines are seen running 

 inwards for a distance of O'Ol mm. from the oral pore. These 

 are the walls of a cylindrical mouth capsule, which later, with 

 the growth of the worm, become much more thickened and 

 obvious. 



Upon the success of the embryo in obtaining a plentiful 

 supply of food depends almost wholly its future growth. If a 

 freshly hatched embryo be transferred to plain water it will 

 live for several days, but show no growth or further develop- 

 ment. Evidently there is only a sufficiency of reserve substance 

 within the ovum to develop the embryo to the time of hatching. 

 When there is enough food, but the medium is very liquid, 



