It is not feasible to monitor such a range of organisms.
We are looking for the most feasible scenario.
It is not feasible to collect on a regular and consistent basis.
Kolliker (Development of Cephalopods, 1844), Remak (Development of the Frog, 1850), and others had laid the foundations of this knowledge in isolated examples; but it was Kovalevsky, by his accounts of the development of Ascidians and of Amphioxus (1866), who really made zoologists see that a strict and complete cellular embryology of animals was as necessary and feasible a factor in the comprehension of their relationships as at the beginning of the century the coarse anatomy had been shown to be by Cuvier.
We are still looking for feasible solutions in new areas of the design space.