THE ANATOMY OF THE COLUMBZ. 233 
Turtur, Zenaida, 
Tympanistria, Zenaidura. 
The ambiens muscle is absent in 
Geopelia, Ptilopus, : 
Goura, Starnenas, 
Phlogenas, Treron. 
The combination of the above-collected facts ought to be of con- 
siderable service in any attempts at classification ; for, leaving the 
number of rectrices out of the question for the minute, of the eight 
possible variations of the three remaining characters, there are seven 
which are found to exist; in other words there are Pigeons known— 
- (1) With an oil-gland, cxca, and an ambiens muscle, viz. Columba, 
Ectopistes, Macropygia, Pterocles, and Turtur. 
(2) With an oil-gland, no cxca, and an ambiens muscle, viz. 
Calenas, Carpophaga, Chaleopelia, Chalcophaps, Chamepelia, Lepto- 
ptila, Leucosarcia, Lopholemus, Haivinpeli, Ocyphaps, Phaps, Tympa- 
nistria, Zenaida, and Zenaidura. 
(3) With no oil-gland, no ceca, and an ambiens muscle, viz. Di- 
duneulus. 
, (4) With an oil-gland, ceca, and no ambiens muscle, viz. Phlo- 
~ geenas. 
(5) With no oil-gland, ceca, and no ambiens muscle, viz. Star- 
nenas. 
(6) With an oil-gland, no ceca, and no ambiens muscle, viz. 
Geopelia, Ptilopus. 
(7) With no oil-gland, no ceca, and no ambiens muscle, viz. 
Treron, Goura. 
The only combination not found being that (8) in which, of the 
three structures concerned, the oil-gland only is wanting. 
The relative value of these different structural peculiarities is the 
point on which their value in classification evidently hinges. The 
number of rectrices being the most variable of them, its importance 
is most probably the least. Next, with regard to the oil-gland, it is Page 253. 
evident that genera such as Treron and Ptilopus are not very far sepa- . 
rated, 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. marie, and absent 
(apparently) in P. melanocephalus. It is also known that among the 
Psittaci this structure may or may not be developed. These considera- 
tions lead me to think that less stress should be laid on the oil-gland 
| than on the two following characters. 
: The constancy of the cxca, as a point of more than family import- 
