“Animals which, though related, are very similar in the adult state, resemble each other more closely in early stages of development, often, indeed, so closely as to be indistinguishable in those early stages. As development proceeds _in such species_, the differences between the two embryos compared become more and more pronounced.” On this point, which is an essential one, I cannot agree with Hurst; for I do not think that the facts show that the early stages of two related forms are necessarily more and more alike the farther back we go. The resemblance that is sometimes so striking in the earlier stages is due to the fewer points there are for comparison, and to the less development of the parts then present. Hurst continues: “If similar comparisons could be instituted between the ancestral species and its much modified descendants, there is no reason for doubting that a similar result would be reached. This, indeed, has been done in the case of some breeds of pigeons, which we have excellent reasons for believing to be descended from _Columba livia_. True, _C. livia_ is not a very remote ancestor, but I do not think that will vitiate the argument. Let me quote Darwin verbatim: ‘As we have conclusive evidence that the breeds of the pigeon are descended from a single wild species, I have compared the young within twelve hours after being hatched; I have carefully measured the proportions (but will not here give the details) of the beak, width of mouth, length of nostril, and of eyelid, size of feet, and length of leg in the wild, parent species, in pouters, fantails, runts, barbs, dragons, carriers, and tumblers. Now some of these birds when mature differ in so extraordinary a manner in the length and form of the beak, and in other characters, that they would certainly have been ranked as distinct genera if found in a state of nature. But when the nestling birds of these several breeds were placed in a row, though most of them could just be distinguished, the proportional differences in the above specified points were incomparably less than in the full-grown birds. Some characteristic points of difference—for instance, that of the width of the mouth—could hardly be detected in the young. But there was one remarkable exception to this rule, for the young of the short-faced tumbler differed from the young of the wild-rock pigeon, and of the other breeds in almost exactly the same proportions as in the adult state.’”