Elizabeth Cary Agassiz, Louis Agassiz: his life and correspondence, third edition

[42] than the air. . . . It is certain that the eggs were already fecundated when we found them in the ground, for later, I found several not so far advanced as those you have, and yet after three weeks I had tadpoles from them. In those eggs which were in the lowest stage of development (how they may be earlier, nescio), nothing was clearly visible; they were simply little yellow balls. After some days, two small dark spots were to be seen marking the position of the eyes, and a longitudinal streak indicated the dorsal ridge. Presently everything became more distinct; the mouth and the nasal opening, the eyes and the tail, which lay in a half circle around the body; the skin was so transparent that the beating of the heart and the blood in the vessels could be easily distinguished; the yolk and the yolk sac were meanwhile sensibly diminished. The movements of the little animal were now quite perceptible,—they were quick and by starts. After three or four weeks the eggs were as large as peas; the bags had burst at the spots where the eggs were attached, and the little creatures filled the egg envelopes completely. They moved incessantly and very quickly. Now the female stripped off the eggs from her legs; she