"As fast as the female deposits her eggs, the male who attends her arranges them on her broad back, to the number of fifty or upwards. The contact of these eggs with the skin appears to produce a sort of inflammation; the skin of the back swells, and becomes covered with pits or cells, which enclose each a single egg, the surface of the back resembling the closed cells of a honeycomb. The female now betakes herself to the water; and in these cells the eggs are not only hatched, but the tadpoles undergo their metamorphosis, emerging in a perfect condition, though very small, after a lapse of _eighty-two days_ from the time in which the eggs were placed in their respective pits." To a tyro in animal physiology it might seem that the smooth rounded egg of a bird or a lizard, presents an example of an organism in the simplest possible condition, and in a stage which, if any can be, is independent of anything that went before. But is it so? Let us see. Here is the egg of the common Fowl. I take it in my hand, and perceive nothing but an uniform, smooth, hard, white surface. This I break, and find that it is a thin layer of calcareous substance, which, on microscopical examination, proves to be composed of minute polygonal particles, so agglutinated as to leave open spaces in the interstices of their contiguous angles. Below this calcareous shell I find a membrane (_membrana putaminis_), which seems, from its thinness in most parts, to be single, but which is separated into two layers at the large end of the egg. [Illustration: HEN'S EGG.] Within this membrane there is another (_the chalaza_) which, closely enveloping the yelk, passes off from it towards each extremity of the egg in the form of a twisted cord. Then comes a delicate membrane (_memb. vitelli_) in close contact with, and enveloping the orange-coloured yelk; which latter carries, on one point of its globular surface, the thin _blastoderm_, or germinal membrane. The yelk-globe, fastened by its twisted _chalazae_, is suspended in a glairy fluid (albumen), which fills the space between it and the _membrana putaminis_. This fluid, though apparently homogeneous, is really composed of many layers, and the innermost of these it is which is condensed into the _chalaza_. Such, then, is the complex structure of this apparently simple object. What light can it throw on our inquiry?