IN the rapidly-shifting condition of our knowledge of the development of all kinds of animals, it is a most difficult thing to produce a satisfactory treatise on Comparative Embryology. None the less ...

IT is scarcely possible to exaggerate the expressions of gratitude which are due from zoologists to Mr. Balfour for the execution of the great task which some three or four years ago he set himself.

All vertebrate embryos follow a common developmental path due to their common ancestry. All have a set of very similar genes (the homeobox genes) that define their basic body plan. As they grow, the ...