Transmission of Homoiogenetic Induction in Presumptive Ectoderm of Newt Embryo

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Abstract
Using newt, C. pyrrhogaster, embryos, the production and/or transmission of a homoiogenetic effect of the induction within a presumptive ectoderm was investigated. The primary inductor was the swimbladder of a crucian carp, Carassius auratus. A piece of presumptive ectoderm was isolated from an early gastrula and 1/3 of its inner surface was placed in contact with the swimbladder for 30 min. After removal of the inductor, the ectodermal piece was allowed to stand by itself for several hours (pre-cultivation), and then it was divided into 3 parts of equal size, i.e., the end that had been placed in contact with the swimbladder (P1), the next middle (P2) and the end part (P3). The tissues produced in each part were examined after 10 days'' cultivation in Holtfreter''s solution. The induction was evoked not only in P1, but also in P2 and P3 which had been free from the inductor. The incidences of tissue differentiation in P2 and P3 increased with the lapse of the pre-cultivation time and the rise in P3 came after P2. Apparently, mesodermal tissues in the parts not placed in contact with the swimbladder (P2 and P3) were evoked by the homoiogenetic stimulus which came from P1 and P2, respectively. P2 of the ectodermal piece was then substituted by an aged ectoderm which had lost its primary competence. In this system, mesodermal induction was not evoked in P3. Production of the homoiogenetic activity of the ectoderm might be associated with its competence.