Identical twins in pigeons arise from ova of markedly aberrant size

Abstract

During 10 years data have been accumulated for yolk size and total egg size in 15,000 to 18,000 eggs of doves and pigeons. Such measurements of these two associated structures permit us, within certain limits, to know some definite things concerning the size of either structure if the weight of the other is known. Another group of 15,000 to 20,000 eggs have been weighed, incubated, and later observations made upon the embryos and young. Incidental to these latter observations 7 instances of identical twins have been found. Such twins other than the seven listed here have almost certainly not appeared; or, if present, they attained a stage of less than 2-day embryos.

The figures of Table I make it clear that at least most of the particular eggs which gave rise to twins were of markedly different size from all other eggs then being produced. This is particularly well shown in the first four instances—given in the upper eight rows of figures—since the twin-bearing egg was in these four cases by far the largest egg produced by its parent during one entire year,—and so much larger as to indicate, in all probability, that it contained the largest ovum produced during the year. The seventh case was likewise of aberrant size—being the smallest of a group of undersized eggs. However, the weights of all eggs obtained in connection with this seventh case, as also with cases 5 and 6, are known to be rather unreliable indices of the weights of the enclosed yolks because the parent birds (K₄6₉, P8₄₃) suffered from special reproductive disorders which involved the production of irregular and inadequate quantities of shell and albumen, unpaired eggs and embryos often incapable of hatching.