The eggs of birds and all other hard-shelled eggs, such as those of the tortoise and the crocodile, are simple solids of revolution; but they differ greatly in form, according to the configuration of the plane curve by the revolution of which the egg is, in a mathôÙeôÙmatôÙiôÙcal sense, generated. Some few eggs, such as those of the owl, the penguin, or the tortoise, are spherical or very nearly so; a few more, such as the grebeãs, the cormorantãs or the pelicanãs, are apôÙproxôÙiôÙmateôÙly ellipsoidal, with symmetrical or nearly symmetrical ends, and somewhat similar are the so-called ãcylindricalã eggs of the megapodes and the sand-grouse; the great majority, like the henãs egg, are ovoid, a little blunter at one end than the other; and some, by an exaggeration of this lack of antero-posterior symmetry, are blunt at one end but charôÙacôÙterisôÙtiôÙcally pointed at the other, as is the case with the eggs of the guillemot and puffin, the sandpiper, plover and curlew. It is an obvious but by no means negligible fact that the egg, while often pointed, is never flattened or discoidal; it is a prolate, but never an oblate, spheroid.
The careful study and collection of birdsã eggs would seem to have begun with the Count de Marsigli1, the same celebrated naturalist who first studied the ãflowersã of the coral, and who wrote the Histoire physique de la mer; and the specific form, as well as the colour and other attributes of the egg have been again and again discussed, and not least by the many dilettanti naturalists of the eighteenth century who soon followed in Marsigliãs footsteps2.
We need do no more than mention Aristotleãs belief, doubtless old in his time, that the more pointed egg produces the male chicken, and the blunter egg the hen; though this theory survived into modern times3 and perhaps still lingers on. Several naturalists, such as Gû¥nther (1772) and Bû¥hle (1818), have taken the trouble to disprove it by experiment. A more modern and more generally accepted explanation has been that the form of the egg is in direct relation to that of the bird which has to be hatched withinãa view that would seem to have been first set forth by Naumann and Bû¥hle, in their great treatise on eggs4, and adopted by Des Murs5 and many other well-known writers.
In a treatise by de Lafresnaye6, an elaborate comparison is made between the skeleton and the egg of the various birds, to shew, for instance, how those birds with a deep-keeled sternum laid rounded eggs, which alone could accommodate the form of the young. According to this view, that ãNature had foreseen7ã the form adapted to and necessary for the growing embryo, it was easy to correlate the owl with its spherical egg, the diver with its elliptical one, and in like manner the round egg of the tortoise and the elongated one of the crocodile with the shape of the creatures which had afterwards to be hatched therein. A few writers, such as Thienemann8, looked at the same facts the other way, and asserted that the form of the egg was determined by that of the bird by which it was laid, and in whose body it had been conformed.
In more recent times, other theories, based upon the principles of Natural Selection, have been current and very generally accepted, to account for these diversities of form. The pointed, conical egg of the guillemot is