=========================+========+============== | | Relative Species | Length | length | in mm. | (in percent) -------------------------+--------+-------------- Ptilogonys caudatus | 134 | 476.9 Ptilogonys cinereus | 111 | 415.6 Phainopepla nitens | 94 | 357.5 Phainoptila melanoxantha | 150 | 457.1 Dulus dominicus | 130 | 451.0 Bombycilla garrula | 102 | 298.2 Bombycilla cedrorum | 95 | 309.5 -------------------------+--------+-------------- Beddard (1898:30) states that caecae in the tract may be highly variable in a single family of birds. The Bombycillidae is no exception in this regard. At the junction of the cloaca and the large intestine, there are two small caecae, the function of which is unknown to me. The caecae are largest in the Ptilogonatinae, smaller in the Bombycillinae, and smallest in the Dulinae. There may be a correlation between large caecae and more insectivorous diet and small caecae and frugivorous diet; however, the data are not conclusive in this regard. ORIGIN OF THE SPECIES It is here postulated that the center of origin for the ancestral stock of the Bombycillidae was in a region of North America, which at the time concerned was temperate or possibly even semi-tropical in climate. Probably Northern Mexico was the place and probably the climate was temperate. It is reasonably certain, because of the distribution of the species of the family, that they originated in the Americas. In the absence of paleontological data (_Bombycilla_ alone is reported, in essentially its modern form, from the late Pleistocene--Wetmore, 1940a), the place and time of origin cannot certainly be determined. The distribution of the family is such that the more primitive groups are in the south. These are the Ptilogonatinae in Central America and Mexico, and the isolated Dulinae in Haiti and the Dominican Republic. This distribution would support the view that the origin was in the south. However, the Holarctic Bombycillinae are so typically birds of northern latitudes that, were it not for such close relatives south of their range, it would appear logical to infer a northerly origin with a subsequent shifting of populations both southward and northward. The phyletic age of the family is probably great, however, as evidenced by the spotty distribution of the birds.