1/4 OSCAR RIDDLE. 



birds is of course very short. On this point, however, I can 

 furnish no observations of value, and can only say that the exact 

 conditions in these forms are not clear. 



It must be left to the further investigations of those who in the 

 course of their studies are able to examine the plumages (particu- 

 larly the plumulaceous ones) of all of the families of birds to 

 decide whether the theory here advanced of the slow rate of 

 growth of the several plumulaceous formations can be universally 

 and absolutely applied. It is the hope of the writer that some 

 one may have the material and the inclination to put this part of 

 the work here reported to a more rigorous test than the writer's 

 limited material has permitted him to do. 



Methods and Materials. 



For the experimental part of the work here reported only a 

 few forms have been used ; but these few animals have been very 

 closely watched and studied. Nearly all the starving experiments 

 were made on the young of the chick {G alius domesticus), and 

 both on the young and old of the ring-doves {Turtur risorhis). 

 For the modifications of the nature of the feather growth the chicks 

 are by far the better material. Control experiments were main- 

 tained throughout. 



It should be said that the under-feeding or " starving " of these 

 animals was usually either accompanied or accomplished by the 

 feeding of the fat-stain Sudan III., which appears to " tie up " the 

 fats of the body. The stain was fed for a purpose not immedi- 

 ately connected with the results reported here, but there is little 

 doubt that it has no specific action on the feathers except in so 

 far as it helps to bring about " starving " conditions in the animal. 



Summary. 



i. The highly modified region of the " down " is in all respects 

 similar to other feather defects or fault-bars which have already 

 been described as occurring at any and all levels in definitive 

 feathers. 



2. Juvenal feathers can by under-feeding be made to persist 

 (chick) in the "downy" conditions practically without growth 

 for several months if the reduced feeding be begun immediately 

 after hatching. 



