After giving a summary of recent literature on the subject, the author then proceeded to state the nature of the material which he had employed in the present investigation.

The bird selected was the common fowl (Gallus domest.), and he had examined a series of microscopic sections through the limbs from the fourth day of incubation to the day of hatching.

The mammalian embryos examined were mice and rabbits, and the fingers of the human fœtus from an embryo approaching the full period of uterogestation.