326 TROPICAL WILD LIFE IN BRITISH GUIANA 



A third tract of large development is the femoral tract. 

 Here the sheaths are nearly as long as those of the spinal 

 tract and pigmented. A slight darkening and lengthening 

 of the scapular tracts may be observed in the young embryo 

 and there are a few long sheaths in the occipital region which, 

 in the later period of hatching, become very long and promi- 

 nent. In the space between the eyes there are two single 

 rows of long, dark sheaths running along the eye grooves. 

 All inferior tracts are indicated only by papillae, there being 

 no noticeable pigmentation or lengthening. 



Ill 



Varied Streaked Flycatcher Empidonomus varius varius 

 (Vieillot) 



PTERYLOSIS 



Unfortunately I have been able to secure only two em- 

 bryos of this bird, both of which are about half developed, 

 though one is apparently a few hours more advanced than 

 the other. Only small papillae are present, there as yet be- 

 ing no sign of pigmentation. Some of the papillae, how- 

 ever, are more prominent than others, and, from the exam- 

 ination of a newly hatched chick, I find that they are the 

 ones that develop into the main down sheaths. 



The positions of the papillae tracts are very similar to 

 those of Pitangus sulphuratus of a slightly more advanced 

 stage, except in regard to the growth of the rectrices. In 

 the present bird these papillae may be seen in their proper 

 place with a corresponding row of coverts above, both show- 

 ing the tiny specks at their tips which are the first indica- 

 tion of pigmentation. The rectrices, themselves, are much 

 larger than their coverts. Directly the opposite is the case 

 of P. sulphuratus in which the coverts develop first, attain- 

 ing a good length and a dark pigmentation before the true 

 rectrices appear plainly as papillae. In the young chick of 



