THE OIL-GLAND. 41 



duct is pyriforra, this has really only a simple orifice, but at the base of its rather wide cavity 1 

 each half of the gland pours out its secretion through a distinct orifice. Whether there are any 

 other cases of the same kind I do not know, but they are certainly very rare ; for in many birds 

 in which I have at first thought that I could detect only a simple orifice, I have afterwards, on a 

 more careful examination, found two apertures, which were certainly small, but nevertheless 

 perfectly distinguishable. ' ' 



I have already mentioned, with regard to Pclecanus, that several external orifices may occur 

 on each half of the gland. In fact, this is the ordinary case in the Water-birds, which possess a 

 short, thick issue, crowned with feathers, such as the Pelarffi, Lonyycnnes, Diomedea, Uria, and 

 Alca. In Ciconia alba, C. nigra, and Diomedea cxulans, there are on each half of the gland five 

 orifices, arranged in a curved line ; in Grus cinerca, Sterna hirundo, Lestris catarrhactes, and 

 Uria troile, I find only three, which in the two last-mentioned species are situated in a pit. In 

 Tantalus ibis numerous o'rificcs on each half of the gland form a complete circle ; and in the very 

 large gland of Pelecanm crispus, the two sets, each of six openings, lie in two parallel longitudinal 

 lines upon its back. 3 In all cases where the oil-gland has several apical apertures, there are the 

 same number of main stems or sacs, in which the gland-ducts open. But if there be only two 

 apertures, one for each half of the gland, each of the latter has also a simple cavity, which contains 

 the secretion poured out by the gland-ducts. This cavity, however, presents many differences. 

 It is sometimes narrow and short, and passes so short a distance into the mass of the gland, that 

 it almost appears to be only a cavity of the efferent nipple ; in other cases, on the contrary, it is 

 much wider and longer. I found it to be largest in the great oil-gland of the Osprey (Pandion 

 haliai : tos), in which it has a very thick peculiar wall, perforated by the orifices of the numerous 

 secretory canals. 



Lastly, the matter secreted by the gland is always of an oleaginous nature, but differs in 

 density, colour, and odour. In most cases it has the consistence of a salve, rarely that of a fluid 

 oil ; its colour is usually whitish, but sometimes brownish ; in Water-birds it is commonly 

 yellow I even remember to have seen it of a saffron colour. As a general rule it is inodorous, 

 but not un frequently has a peculiar but variable odour; that of Anas moschata, as already 



1 In this cavity, which is kept extended by the tubes of the feathers of the circlet situated 

 in its wall, the secretion of the gland, which is at first yellow, but afterwards becomes blackish, 

 collects iu the female (but only in this sex, and not in the male, who does not take part in 

 incubation, although he does assist in feeding the young), and is the cause of the powerful odour 

 which the Hoopoe diffuses about this period. This odour is given off only by the females and 

 the young ; by the former as long as they are sitting and feeding their young, by the latter as long 

 as they remain in the nest. Is this odour intended to protect the females and young from the pursuit 

 of predaceous animals ? 



2 Joh. Miiller (loc. cil.) describes in the gland of the Swan two large apertures, surrounded by 

 numerous smaller ones. The latter, however, are by no means glandular orifices, but the holes in which 

 the feathers of the circlet are inserted. As the gland examined had been preserved in alcohol, these, 

 as usual in such cases when the fluid is not strong enough, had become loose, and fallen out, in con- 

 sequence of incipient putrefaction. The swan (Cygnus], like all the Unguirostres, has only one rather 

 wide aperture in each half of the gland. 



6 



