A morphological study of skeletogenesis in malathion-treated chick embryos

Chick eggs were injected with 0.1 ml of 2% malathion in corn oil on days 3, 5, 7, 9 and 11 of incubation. All embryos were collected on incubation day 14 and the effects of this treatment on their general morphology and on the calcification of bone were studied. Surviving embryos were weighed and measurements were taken of body, leg and mandible lengths. The 3-day old chicks treated with malathion, suffered the highest mortality rate, followed by those embryos injected on days 5, 9 and 11 of incubation. Embryos injected on day 7 of incubation demonstrated the lowest mortality rate. Anatomically, the treated embryos exhibited reductions in body weight and in body and leg lengths. These reductions were most severe in those embryos treated at the 3-day incubation stage. The whole embryos were prepared with the Alizarin red S method to demonstrate calcification. The malathion Caused a delay in the mineralization of some endochondral bones. Its major effects were primarily on those bones involved in active chondrification.