Testoviron is a potent inducer of chick blastoderm

Testoviron is a potent neural inducer, acting on the epiblast of the chick embryo during the period of competence (Hamburger-Hamilton stages 3 and 4). Under the influence of Testoviron, the epiblast differentiates in the neural direction. The structure that develops is typically neural in appearance with a 'dorsoventral' and a mediolateral pattern. The notochord is not formed; consequently, there is no lengthening and therefore no craniocaudal pattern. Hence, Testoviron is an 'inducer' and not an 'evocator' even though it differs from the 'primary organizer' in that it does not organize the neural groove in the axial direction as does the dorsal lip of the blastopore of the amphibians or as with Hensen's node in birds. Therefore, it would be very interesting to ascertain whether there is a biochemical difference in the constitution between Hensen's node and the notochord of the bird. The inducing action is localized in a small region aroung the testoviron implant. The steroids might be of major importance in the early morphogenetic processes. We feel steroids deserve more attention than they are receiving at the present time.