History and Objectives: Due to importance of developmental studies and specially fingers formation and since recent reports indicated a role for apoptosis in the development of free fingers, the present study was carried out to on chick embryo with free fingers as the experimental group and duck embryo with interdigital membrane as control group.

Materials and Methods: An analytical cohort study on white Leghorn eggs and Royal Pekin duck eggs were carried out. Chick embryos were at sixth and 9th days of incubation (Stage 29-35) and duck embryos at eight and half and 11th day of incubation at 12 hour intervals were taken for study. In the present study, neutral red as a vital color by Hinchiffe & Ede method was selected. The staining is specific for apoptotic and macrophage cells. Embryo legs were monitored by stereomicroscope and pattern of apoptosis were followed.

Results: Interdigital cellular apoptosis was observed in chick and duck embryos at 6.5 days and reached a pick level at 7.5 day and ended at 8.5 day when interdigital tissue had complete regression. Interdigital tissue apoptosis for the four fingers of foot was obvious in chick as well duck embryos however the extent of apoptosis was less in duck embryos. Interdigital cellular apoptosis started at the 9th day and continued until the 9.5 day and terminated at 11th day. Interdigital membrane between the first and second finger show similar necrotic region whereas the fingers formation is quite different.

Conclusion: Apoptotic pattern of interdigital membrane of chick and duck is accompanied by removal of mesenchyma and sculpturing and separation of fingers. Comparison of apoptotic intensity reveals other possible factors for the separation of fingers. It is suggested that extended study should be carried out to unravel the mechanism of interdigital regression at cellular as well as genetic level.