128 PTERYLOGRAPHY. 



family, and differ both in number and position. When only two are present, as in Eurypyga, 

 they are situated on the back near the hinder part of the dorsal tract, and reach from the rump 

 nearly to the shoulder-blades, each resembling half an ellipse (Plate VIII, fig. 15). But if there 

 are four tracts, as in the Bitterns (figs. 10 and 11), one pair is situated in the same place, but is 

 much smaller, and limited only to the posterior pelvic region. Each tract is elliptical, and so 

 broad that the entire hinder part of the thigh is covered by it. The other pair occurs on the 

 ventral surface, and consists of two elongated elliptical bands, which exactly follow the course of 

 the furcula, and separate the cervical from the pectoral portion of the inferior tract. Lastly, when 

 six powder-down-tracts occur, as in all other Erodii, there are, besides the two pairs just de- 

 scribed, a third pair, consisting of two small and very narrow bands, which are placed on the 

 ventral surface in the inguinal region, near the outer margin of the stem of the inferior tract. 1 



1. Ardea (Plate VIII, figs. 10 12). The pterylosis of the head is uninterrupted, but in the 

 circumference of the ear there is a circular space, which is very distinct in the Bittern. Imme- 

 diately at the occiput commences a broad space, which runs down on the back of the whole of 

 the neck, and accompanies the spinal column to the oil-gland. On the lower surface the head- 

 plumage extends a little beyond the angle of the jaw, and then divides into two narrow limbs, 

 which turn outwards, and run down exactly on the sides of the neck. I therefore call them 

 lateral neck-tracts. Having a breadth of three or four rows of feathers as far as the point just 

 mentioned, they there suddenly become narrow, and extend as uni-or biserial bands more towards 

 the dorsal surface of the neck, pass in the same condition on to the fore part of the trunk, and 

 then, gradually becoming broader and stronger, run on between the shoulder-blades, but terminate 

 before attaining the extremities of the latter. 



These two tract-bands may be regarded as the scapular part of the dorsal tract, and we may 

 suppose that the spinal space, which usually reaches only to the shoulder-blades, or at the utmost 

 passes on to the commencement of the neck, has here, been prolonged up to the head. This 

 circumstance would then be the most remarkable peculiarity in the pterylosis of the Herons. 

 From the extremity of the tract just described commences the hinder part of the dorsal tract, 

 which is deeply cleft as far as the oil-gland : it is usually separated by a small gap from the anterior 

 part, and at first consists only of one or two rows of feathers. Immediately in front of the oil- 

 gland it becomes simpler and very broad, nay, even dilated, so as to cover the whole basal portion 

 of the tail. The above-described lateral neck-tracts are, however, equally the commencement of 

 the inferior tract, and result essentially from the union of the limbs both of the dorsal and 

 inferior tracts, which are divided up to the head. Hence the truncal portion of the inferior tract 

 also issues from the extremity of the lateral neck-tracts, runs on to the breast as a narrow band 

 of three or four feathers in width, is even more or less diminished at the end of the musculus 

 pectoralis major (A. nycticorax), and becomes both weaker and narrower on the belly. In the 

 Bittern the pectoral portion is anteriorly united only with the axillary tract, and through this 

 with the anterior part of the divided dorsal tract before the latter passes into the lateral neck-tract, 

 which is distinctly set off from it, so that, when seen from below (Plate VIII, fig. 10), it appears 

 as if the inferior tract were entirely separated from the lateral neck -tract, which, however, is not 

 the case. The lateral neck-tract rather forms at its extremity a short inner branch turning 



1 For some additional remarks on the powder-down-tracts in this group and its allies see 

 Appendix I, note 2. P.L.S. 



