1874.] ANATOMY OF THE COLXJMBjB. 253 



is most probably the least. Next, with regard to the oil-gland, it is 

 evident that genera such as Treron and Ptilonopus are not very far 

 separated, notwithstanding that there are important differences between 

 them ; yet the former wants the oil-gland and the latter possesses it, 

 though but feebly developed in P.jambu and P. marice, and absent 

 (apparently) in P. melanocephalus. It is also known that among 

 the Psittaci this structure may or may not be developed. These 

 considerations lead me to think that less stress should be laid on the 

 oil-gland than on the two following characters. 



The constancy of the caeca, as a point of more than family import- 

 ance in all other birds, would lead me to consider their presence or 

 absence as more significant than that of the oil-gland. 



In my last communication to this Society* I gave reasons to show 

 that the presence or absence of the ambiens muscle was a very signi- 

 ficant fact in the classification of birds generally. This would lead 

 me to lay considerable stress on the same point in any order or sub- 

 order in which it is found to vary. 



Assuming then, as in my last paper, for reasons there stated, 

 that the ancestral Pigeon possessed the ambiens muscle, and, on the 

 same grounds, that it had caeca coli and an oil-gland, it is evident 

 that the Pteroclidae, together with Columba, Turtur, Macropygia, 

 and Ectopistes have departed least from the ancestral type. The 

 Pteroclidae have branched off in another direction, as will be subse- 

 quently shown ; and therefore Columba, Turtur, Ectopistes, and 

 Macropygia (together with those undissected genera unmistakably 

 allied to them) may be considered to be the least modified, and 

 therefore most typical of the Columbae. 



From these, if the peculiarities of the ambiens muscle have the 

 importance which I assign them, a branch sprang, in which the 

 ambiens was undeveloped. This includes at the present day Star- 

 noenas, Phlogcenas, Geopelia, Ptilonopus, Treron, and Goura, most 

 of which possess 14 rectrices, and are confined to the Malay archi- 

 pelago. This Treronine division, as it may be termed, seems to be 

 preserved in its primitive form in Phlogcenas, in which no further 

 structures are lost. Starncenas, which, notwithstanding its peculiar 

 distribution, must be considered as a member of it, loses the oil- 

 gland, and Geopelia, as well as Ptilonopus, the caeca, whilst Treron 

 and Goura are deficient in both. 



The main stem seems to have shortly given off a second branch, 

 in which the caeca coli were alone wanting. This Phapine branch is 

 now represented, without further complication, by Calanas, Carpo- 

 phaga, Chalcopelia, Chalcophaps, Chamcepelia, Leptoptila, Leuco- 

 sarcia, Metriopelia, Ocyphaps, Phaps, Tympanistria, and Zenaida ; 

 whilst from it has sprung Didunculus, without any oil-gland and 

 with its quaint beak and remarkably long intestinal canal, which 

 would indicate that its diet was usually one of fish, or more probably 

 molluscaf. 



* P.Z. S. 1874, p. 111. 



t It is through the kindness of Prof. Newton that I have had the opportu- 

 nity of dissecting a specimen of this rare bird. 



