Experiments concerning the initiation of the choroid fissure in Gallus domesticus

121 experiments are reported in Gallus domesticus, in which the left optic primordium from donor embryos ranging from stages 9 to 17 (Hamburger & Hamilton) was grafted upside down into host embryos at approximately stage 11-(12 somite stage), replacing the host right primary optic vesicle, which had previously been removed. In 36 experiments, up to donor stage 12+, the choroid fissure in the graft developed in hostwise ventral orientation, i.e. from the original dorsal quadrant of the graft. In four cases no fissure appeared. In donor stage 17 grafts, the fissure was invariably in graftwise dorsal orientation. In the intermediate donor stages 14 and 15, hostwise fissures occured in 12 out of 23 experiments, and in the donor stages 15 and 16, in 7 out of 28. Six cases were seen in which the fissure was in a position approximately midway between the hostwise and graftwise positions. Multiple fissures were not encountered. The results are compared with those reported in Trition by Sato (1933).