T IIE curious fluffy, greasy tracts of feathers found in patches on the breast and pelvic region in herons and occurring at random in various other groups of birds, even in the Passeriform order, have been the subject of considerable speculation and comment. Some time ago I had opportunity to study their development in the young of a few species of herons and from these observations was able to settle definitely their function so far as con- cerns this group of birds at least. Observations were made first while rearing a young Great Blue Heron (Ardea h. treganzai), and were checked and verified in the young of the Snowy Heron (Egretta c.. candidissima), Black-crowned Night Heron (Nycticorax n. naevius), and Bittern ( Botaurus lentiginosus). It is interesting to note that my findings verify a possible function of these tracts as suggested by Newton and Gadow (Dictionary of Birds, 1896, p. 654). In the young Great Blue Heron powder down tracts produced functional feathers soon after the contour and flight feathers had burst their sheaths and the bird began to preen and caxe for its plumage. The heron in question had been taken from the nest while still too young to know fear of man, and as I reared it by hand it became devoted to me, though fierce and truculent toward all others. As its plumage developed I noted that the bird constantly rubbed the bill in the powder downs, and on examination found that the heron was uti- lizing the greasy, powdery substance given off by the tracts to dress and oil the contour feathers. The bill was worked in among the powder downs until a small amount of the exuviae had gathered at the tips of the mandibles and then contour or wing feathers were pulled rapidly through the bill, anointing them with this oily substance. At once return was made to the powder' downs after which other feathem were treated in turn until the whole of the body and wing plumage had been properly dressed. ! had no difficulty in observing the process as, when permitted, the heron until practically grown dlighted in standing upon my knee as ! sat in a chair. I was able to place my fingers in beside the tip of the bill, in the powder downs, to feel the mandibles gently nibbling at the downy feathers and then to see the bill withdrawn with its sides covered witk the grayish powder. Following this I observed as it was passed over other feathers. This process was repeated daily whenever I cared to see it. At the same time I discovered by examination that the nropygial gland. the usual source of oil for feathers seemed undeveloped and remained iu a non- functional condition until the heron was practically grown. The bird in early life paid no attention to this gland but worked in either pelvic or pectoral down patches. The actual development of the oil gland I did not observe as the heron at this stage became so vicious toward others that I was forced to discourage its tameness until finally it left the laboratory. When attention was attracted to this peculiarity in the Great Blare Heron I took occasion to examine other young herons and found a similar condition existing in Snowy Herons, Black-crowned Night Herons and Bitterns. The accompanying illustration (fig. 36) shows well the relative size of the powder down tracts and the non-functional oil gland in a yeung Great Blue Heron (A. b. trcganzai) about two-thirds - p Fig. 36. POq)ER DOVN PATCHES AND U'ROPYGI- AL GLAND EROM GREAT BLUE HERON AllOUT T,O-THIRDS GROVN, DISSECTED ROM FRESII .,PECIMEN TO [I{)  RELA'IIVE SIZE. P PEC- TORAL POVDER I)ON TR ('q'S; P' PELVIC TRACTS; ['] DEVELOPING lqIOPYGI AI, GLAND (NO]' YET FUNCTIONAL). grown. The oil gland is the sulall rounded object at one side be- tween the two pelvic tracts. Iu another cul (fig. 37)the young Great Blue Heron is shown secur- ing the greasy material froin the powder down patch ou one side of the breast. Parenthetically I may add that although on various occasions I exmnined powder down tracts iu living and in dead herons I xvas unable to observe that these tracts were luminous, in spite of rimher- ons records on the part of others, to the contrary. Since anaking these notes on pow- der downs it has been any inten- tion to go farther into this subject and to study the development of these feath- grs and also of the oil gland. As a natter of fact powder dowus are so little un- derstood that ordinary definitions of them in text-books are vague aud uncertaiu and their recognition in certain groups of birds is at times difficult. Wherc these downs are not segregated in defilfite tracts but are diffused through the pterylae it is possible, without careful attention, to confuse them with other feathers thai have just begun to break their sheaths when in process of devel- opnent. Similarity in fUllctim between po;vder downs and oil gland has sug- gested that these two organs inay be homologous in origin. Should it prove that the powder dmvn tract is a prinitive arrangement from which the nore complicated oil gland has developed then we may have a ready explalmtion for the occurrence of powder downs apparently at raudmn in such diverse groups as Tinamous, the Whale-headed Stork. the Kagu. Sun Bittern, Mesite. herons and bitterns, the diurnal birds of prey (where they may be found in many other species than currently recognized), parrots, Frogmouths, Potoos, Leptosoma and lastly in the Wood Swallows among the passerines. The struct- ure of the oil gland with its nunerous coiled tubes secreting fluid into a com- mon chanber which in turn discharges the oil through one or many orifices Fig. 37. IBIMATt'RE GREAT BLUE I-IERON OILING MANI}I- BIJE,'$ BY VORKING TIIEM IN P(),q}ER DO,N PATCIIES PRE- PAPATORY TO PIIEEIqlNG CONTOUR FEATIIERS. to the surface might suggest an origin through the amalgamation of a number of separate tubes opening separately. All this. however, is pure hypothesis that may be verified or overthrown by careful study of the enbryology of these structures. Biological Surrey, Washington, D.C., May 26, 1920.