210 MR. W. A. FORBES ON THE [Feb. /, 



It is not unusual iu birds to find a small irregular nipple-like 

 projection guarding the entrance to the pylorus ; aud it is, I am in- 

 clined to believe, a greatly developed condition of this structure that 

 forms the hairy " plug " of the Old- World Darters. 



In the rest of its anatomy Plotus melanog aster resembles in nearly 

 CTcry respect P. anhinga aud P. levaillanti. As in the latter, there 

 are two caeca, "2 inch long, whilst in most specimens of P. anhinga 

 one only has been observed'. As in P. anhinga, the large intestine 

 is peculiarly long, measuring 5*5 inches ; the small intestine has a 

 length of 30 inches. The bursa fahricii, I may add, in the present 

 specimen (a (5 ) had the ordinary relations of that organ to the 

 cloaca, opening into that chamber by a small pore. There is only 

 one carotid artery, the left, as in the two other species of Plotus, the 

 genus Peleeanus, and Sula leucogastra and S.piscator, though not in 

 S, bassana, or the other Steganopodes. The patella is only grooved, 

 and not perforated, by the ambiens muscle. 



The structure of the neck in P. melanogaster is almost identical 

 with that of P. anhinga, as described and figured by Garrod. 

 " Donitz's bridge," situated, as in the other species, on the 9th 

 cervical vertebra, is well-ossified in the present specimen, as it 

 is also iu P. levaillanti and P. novcB-hollandice, though not in 

 P. anhinga. 



In addition to this, the similarly-situated fibrous bands — formed by 

 a specialized part of the general cervical aponeurosis — on the 11th 

 cervical vertebra, which are correctly figured and described (in the 

 explanation to the plate) by Garrod ^ in P. anhinga, are also ossi- 

 fied, each in its median portion being converted, over a small area 

 about the size of a hemp-seed, into bone. Through the canal thus 

 formed on each side, the longus colli posterior, as well as the 

 general mass of posterior neck-muscles, passes. On examination 

 of P. levaillanti, I find these bands also ossified in that species ; 

 in P. anhinga, as already correctly stated by Garrod, they remain 

 fibrous. There is no such ossification of the cervical portion of the 

 longus colli posterior tendon in this species, as was observed by 

 Garrod in P. anhinga ; and in this respect again the African and 

 Indian species agree, and differ from their American relative. 



Prof. Garrod, iu the first of his papers already referred to, has 

 fully aud accurately described the peculiar osteological and myolo- 

 gical characters of the neck of the Darter. But, probably from never 

 haviug observed these birds when feeding, he has not pointed out 

 the connexion between this peculiar neck, with its naturally persis- 

 tent " kink," of the Darters and their mode of life. 



The Darters feed entirely, so far as I have been able to observe, 

 under water. Swimming with its wings half expanded, though loco- 

 motion is effected entirely by the feet, the bird pursues his prey 

 (small fishes) with a peculiar " darting " or jerky action of the head 



' In a specimen of Plotus anhinga that has passed through my hands since 

 this paper was read there was, in addition to a single cseciim of the ordinary 

 size, a much more rudimentary one developed on the other side of the intestine. 



^ L. c. pi. xviii. fig. 2 a. 



