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Jan., 1910 A DEFENSE OF OOLOG 21 but a single set, or the very remarkable "purplish eggs" of the California Jay (A?bltelocoma californica californica) which are so entirely different from the usual brown-spotted green specimens. I happen' to have found but two sets of this type. Mr. H. A. Snow of Newark also terms them rare, while Mr. H. W. Carriger states he has found them commonly in the vicinity of Sonoma. In 1894 I collected a set of eggs of the Black-headed Grosbeak (?7an?elodia ?nelanoce151tala) of a type I have never seen since, having an almost white ground color lightly spotted with bright rusty-brown. In 1890 I took an egg of the California Towhee (Pi?bilo crissalis crissalis) which for glossiness I have never seen equaled among eggs of this species. In fact the texture and thickness of egg shells should also be lookt into more carefully; for it seems that altho the food of birds is widely different, yet each species is enabled to secrete sufficient material for a protective covering for Fig. 11. T?VENT EGGS OF THE BRE?VER BLACKBIRD, SELECTED FRO?! NINE SETs TO ?HOgV ARIATION 1N COLOR AND SHAPE; SOl?E?'HAT REDUCED IN SIZE the embryo Whether this lime-shell nmterial is in some cases derived solely from food, or from water alone is an interesting question In some sections, as the higher Sierras, the water being snow-water is almost pure. Analysis of the foods of birds would perhaps show what percentage of lime could be obtained from them. From my own observation I would say that the thickness of egg-shells seems solely due to the intention of Nature, for I have failed to discern any difference in eggs of the same bird from different localities; while on the other hand, as in the case of the Cliff and Rough-winged Swallows, we have both hard and soft-shelled eggs in birds of the same family--breeding in the same locality and living on the same or very similar diet. I am not aware whether it is a common characteristic of them or not, but the eggs of the Rock Wren (Sal?bincles obsolett?s) which I took on the