AbstractPortions ofFundulusembryonic shields, usually posterior or anterior halves, were partially dissociated into cell clumps and separate cells by exposure to salt solution lacking magnesium and calcium ions; the dissociates were reaggregated in salt solution containing these ions, then immediately grafted to extraembryonic regions of host gastrulae. Technical difficulties prevented complete dissociation of the shield portions and complete retrieval of the dissociates, but a number of hosts bearing secondary complexes differentiated in association with the grafts developed successfully to late stages.Complexes associated with grafts derived from posterior shield portions frequently formed tails, and differentiated, with few exceptions, the same range of structures described earlier as having differentiated when either unfragmented or mechanically minced shield portions were grafted. In the parts of the new graft complexes remaining attached to the yolksac epithelium, the secondary structures formed were often in topographic disarray, but in the free tails that grew out from these complexes, the axial structures frequently attained normal topographic relationships.Complexes associated with grafts derived from anterior shield portions frequently formed, among other structures, highly differentiated eyes, often with normal retinal stratification, sometimes accompanied by lens, cornea, iris, or optic nerve.The high degree of organization of tails developing in association with grafts of posterior origin, and of eyes in association with grafts of anterior origin, is possibly explicable not by cellular self‐sorting and self‐assembly, but rather by embryonic field phenom