PteryJography of the Hoatzin. 365 



VI. Literature of the Plerylosis of Opisthocomus. 



Let us now turn to the literature of the subject. Happily 

 this is not extensive. 



Nitzsch was, I believe, the first to describe and figure the 

 pterylosis of Opisthocomus. On examining his figure we 

 find the bare, brightly-coloured skin on the sides of the face 

 represented as if restricted to a relatively small area, partly 

 surrounding the eye from below. The spinal tract starts, 

 he tells us, '^ as a strong triserial band * from the midst of 

 the plumage of the lower pai^t of the neck, and divides be- 

 tween the shoulders into two limbs, with which tlie originally 

 divergent feather-rows of the biserial hinder part are united 

 at the end ; from the caudal pit onwards it becomes some- 

 what broader, and encloses the oil-gland.^' The ventral 

 tract, we are told, " commences as two broad bands, which 

 run down close to the keel of the sternum, and become some- 

 what stronger at the outer margin At the end of the 



sternum these are narrowed, and pass on, gradually becoming 

 weaker, to the anus, at which they terminate with a breadth 



of only two feathers In the wing there are nineteen 



remiges, of Avhich ten are on the pinion.''^ 



The next reference to the pterylosis of Opisthocomus is 

 that by Mr. J. B. Perrin (9), who, after an examination of 

 some " spirit-specimens," seems to have persuaded himself 

 that "the pterylography was almost identical with that 

 figured in Nitzsch^s work." As Mr. Beddard (1) has pointed 

 out, the word '' almost " in a question of pterylography 

 '^ allows a considerable latitude for variation." Perrin has 

 illustrated this portion of his paper with Nitzsch^s figures, 

 much enlarged, and not quite correctly copied. 



The late Prof. Garrod (5), referring to NitzscVs repre- 

 sentation of the pectoral region of Opisthocomus, suggested 

 that it was due to " an accidental error," and that he ''evi- 

 dently had an imperfect skin to work upon." He next 

 describes the sternal callosity as "an oval area, about 0"75 

 inch long from above downwards, and 0-25 inch in breadth, 



* Composed of three longitudinal rows of feathers. 



