Three developing embryos at each day of the preceding days of incubation
for each experimental and control groups were used for determination of morphological examination and mitotic index as kinetic parameter of the cell cycle in two regions of the nervous system and skin .The region of the nervous system was the spinal cord. For histological preparation and studying, embryos were rinsed in saline water and fixed in Bouin’s fluid for 24 h as described in the method of Gabe (1976). Fixation consists of the following compositions: saturated aqueous solution of picric acid 100 parts, formaldehyde solution 25% parts and five parts of glacial acetic acid were added promptly before using. This solution acts as a fixative and/or preservative. After fixation, embryos were thoroughly washed with 70% ethyl alcohol. Then they were dehydrated through an ascending series of alcohol then cleared in xylene and embedded in paraffin. Paraffin blocks were treated, fixed over the block holder of the microtome and serially sectioned at 4 and 5 u. The obtained paraffin ribbons containing the serial sections were cut into pieces of 5 cm long and mounted over a slide placed over a hotplate adjusted at 40 C. The mounted