500 PROCEEDINGS OF TEE NATIONAL MUSEUM. vol.47. 



Other irregularities are apparent in the molt of the bird as in four 

 specimens from eastern Sumatra taken from September to February 

 one or more primaries is found to be in an undeveloped condition, and 

 variation is shown in the renewal of the shorter pairs of lateral 

 rectrices. 



To summarize, in the Giant HornbiU (RMnoplax vigil) but one 

 feather of the central pair is developed at one time and this spike, 

 much longer than the other rectrices, on reaching maturity, remains 

 in position for more than a year, probably for two. Its companion, 

 beginning its growth after the other has gained its extreme length, 

 then equals it in size. The first feather is then molted and is gradu- 

 ally replaced by another, so that in the renewal of this central pair 

 there is a continual alternation instead of the usual method by which 

 these feathers are renewed synchronously on the right and left sides. 

 It is difficult to determine how this peculiar situation has been brought 

 about, but it is apparently an interesting case of aberrant evolution.* 



Upon the facts as outlined above, we may, however, base the hypo- 

 thesis that originally a HombiU with tail feathers more or less equal 

 in length, through some accident retained a central feather which 

 grew, outstripping its fellows until it had more than doubled their 

 size and then later was cast off. In the meanwhile its companion 

 attained an equal length, reaching maturity before the fall of the first 

 feather and, remaining in position, maintained the peculiar spike-hke 

 form unique in this genus among the HornbiUs. That this change 

 has been rather recent is testified by the fact that these long central 

 feathers have a broad white tip and a black subapical band conform- 

 ing exactly in width and color to the bands found on the shorter 

 lateral feathers. 



1 Since this was written thiree additional specimens of tliis HombiU, collected by Mr. H. C. Raven, 

 have been received from Borneo, as follows: Cat. No. 182804, U. S. N. M., adult male, Sungei Karangan, 

 October 28, 1913; Cat. No. 182805, U. S. N. M., young female, Sungei Karangan, December 8, 1913; Cat. 

 No. 182806, U. S. N. M., adult male, Sungei Pelawan, January 5, 1914. 



The two adult males exhibit the same peculiarities as the series discussed above. In each bird one of 

 the central rectrices is worn and abraded, while its companion is bright and new. In the October speci- 

 men the new feather is three inches shorter than its older companion, while in the January bird the two 

 are about equal, and the older feather would soon have been dropped. 



Great Interest, however, attaches to the development found In the immatiu-e specimen. This bird is 

 about three-fourths grown, the primaries are still shorter than the secondaries and are worn and dirty , as 

 though the bird had recently left the nest, and the huge knob on the culmen is in the early stages of 

 growth. In the tail the same condition is noted as in the adults. The right feather of the central 

 pairof rectrices is worn and broken, one third being gone. The left rectrix while worn is evidently a 

 newer feather. As in the adults the new feather grows out under the old one. From this it is evident 

 that a single median tail feather grows out to full length while the bird Is still in the nest. Whether 

 another feather appears with it to be pushed out by one following later can be determined only from 

 more material. 



