The case is different, however, with the fruit-eating birds. The fruits they consume are retained but a comparatively short time in the crop, pass hurriedly through the gizzard, and no doubt carry along with them some of the smaller seeds of berries, and now and then the pit of a cherry or small plum. The gizzard, in these cases, is simply gorged with the pulp and juices of the fruit, its muscular action more or less relaxed, and some of the seeds consequently escape the grinding process they would otherwise undergo. And yet we are satisfied that a majority of these seeds even, are more or less thoroughly triturated by a healthy gravel-eating bird. This would certainly be the case if they were retained for any length of time in the pyloric division of the bird's stomach. All birds have gizzards, but their grinding capacity depends very much on the character of the food they eat. Birds of prey, and others subsisting mostly or entirely on animal food, have thin, membranous, and comparatively flabby gizzards; while those living on hard grains and seeds have extremely thick, powerful, and muscular ones,--those capable of crushing up and thoroughly triturating all the food they take into their crops. These gizzards are nature's gristmills, and they grind exceedingly fine. If any seed escapes, it is because the mill has been flooded by the bird, and not because of any defect in the grinding apparatus. These birds are not, therefore "natural sowers of seeds," as Professor Marsh and some others claim; but are, at most, only accidental or chance-sowers. Nature never designed that they should do anything more than consume the food they eat, or submit it to the proper action of their digestive organs. It might as well be claimed that the secretary bird is a "natural sower of serpents," as that many of the grain-eating birds are "the natural sowers of seeds." The theory is too foraminated--too full of loopholes and unsatisfactory conditions--to be accepted as an explanation of the more general phenomena presented. The fruit-eating quadrupeds are, relatively, far better sowers of seeds than the birds, for they eat fruit without sending their grists to mill. Dr. Dwight rejected the transportation theory as early as 1820, and Professor Marsh gives any number of cases where it was necessary for him to abandon it. And yet some of our ablest writers, publishing works of quite recent date, adhere to it as the only theory that accounts for all the phenomena presented.