We collected about two hundred eggs of this species, nearly all of them at Rosario de Lerma, and a great variation in marking exists; there is also some difference in color. As a general rule the eggs are greenish or bluish, rather heavily spotted with reddish-brown; in a very few specimens the background is of a pale flesh-color, and in a small number of others it approaches white, having, however, a dull grayish tinge; of the entire lot, four only are so lightly marked as to appear unspotted. Not a single egg is pure white or has a pure white background (my standard of comparison is an egg of the oven-bird) “like the eggs of birds that breed in dark holes”; the majority of these eggs were taken from the darkened interiors of oven-birds’ nests. A type of egg not uncommon is heavily and evenly marked all over with fine dots and larger spots of reddish-brown. Judging from the material at hand I should say that there is a characteristic type of marking running through the eggs of the species if we except the two extremes, _viz._, those almost unspotted, and those so entirely covered with heavy blotches that they appear to be of a uniform chocolate color. However, the eggs of each individual seem to vary in some respect from those of any other, as it is impossible to find two exactly alike in comparing series from different places. Frequently, two or more eggs found in the same nest resemble each other so closely in size, shape, and coloration, that I think it reasonably safe to say that they were laid by the same bird. The nests of the smaller birds contained from one to four eggs of these parasites, in addition to those of the rightful owners. On January 12, I opened an oven-bird nest and was surprised to find fifteen cowbirds’ eggs in the dark interior. This I considered a record, but Boyle brought one in on the same day containing twenty-six of the speckled eggs. In the days that followed, we discovered numerous “sets” of from ten to twenty. The nest that contained the final record number was found January 16, it contained thirty-eight eggs--one of the oven-birds and thirty-seven of the cowbirds. Later, we again met these old acquaintances wintering in the rice-fields and rush-grown marshes of Tucuman. The white ani (_Guira guira_) or Guiraca, first seen near Asuncion, and later in Bolivia, was plentiful at Rosario de Lerma. The bird was usually found in small flocks and fed on the ground. We found several of their nests near Rosario de Lerma. They were large, loosely built of sticks and placed in the crotch of a cactus or other thorny plant, at no great height from the ground. However, the nest is not conspicuous in spite of its size.