OCR Text |
Show 258 MR. A. H. GARROD ON THE [May 5, their structure. A more extended series of observations may indicate reasons for modifying the stress laid on some of the points ; but it cannot, if my. dissections are correct, change the facts themselves. As an instance of the direction in which alterations may be shown to be required, the case of the relation of Ptilonopus and Treron may be taken; for, notwithstanding their general similarity in structure, these two genera present important points of difference. In the possession of a gall-bladder by the former, it resembles Carpophaga ; and it is quite possible that the similarity of the two genera under consideration is the result of similarity in habit only, and that whilst the latter (Treron) sprang from the Treronine stem direct, the former (Ptilonopus) m a y have descended from the Phapine stock. This appearance of the gall-bladder in these genera is very difficult to explain, except on the supposition that in those in which it is absent it has been lost very lately, or that Carpophaga and Ptilonopus are very intimately related forms. The uncertainty of its appearance in closely related genera of Mammalia reduces its value as a character of classificational importance among them; but its very general absence in the Columbae makes it almost impossible not to lay considerable stress, in classification, on its presence. In the accompanying Table Ptilonopus is placed in the same division with Treron because of their similarity in the points there laid stress on; but it requires a very inconsiderable amount more evidence to necessitate its being removed from there into close proximity with Carpophaga and Lopholamus. The fact that two forms in many respects so similar should differ so much in others is of itself a strong argument in favour of their separation; for the probability that forces which tend to produce marked external resemblances should simultaneously develop internal differences is, to say the least, extremely small. Suborder COLUMBAE. Schizorhinal birds with a characteristic pterylosis, humerus-head, and sternum ; with the fourth gluteal muscle, which in other schizorhinal birds covers the femur-head, undeveloped ; with the oil-gland nude, when present, and with the gall-bladder generally absent. Family COLUMBIDAE. Columbee in which the intestinal caeca never exceed half an inch in length.] Subfamily COLUMBINE. Columbidae possessing the ambiens muscle, intestinal caeca, an oil-gland, no gall-bladder, and 12 rectrices. Genus Columba. „ Turtur. „ Macropygia. „ Ectopistes. Subfamily PHAPIN^E. Columbidae possessing the ambiens muscle and no intestinal caeca. |