 The laws received a mixed appreciation.While they were criticised in detail, they formed the foundation of modern embryology.The British zoologist Adam Sedgwick studied the developing embryos of dogfish and chicken, and in 1894 noted a series of differences, such as the green yolk in the dogfish and yellow yolk in the chicken, absence of embryonic rim in chick embryos, absence of blastopore in dogfish, and differences in the gill slits and gill clefts.