Experiments on the Determination and Development of the Pronephros of Amblystoma Punctatum

Abstract

This investigation deals with two problems; first the time at which determination of the pronephros occurs and second, the question of the transplantibility of this organ and its relation to the various problems of development and function.

Prospective pronephric mesoderm from embryos of early stages was transplanted to the flank region of animals in the early tail bud stages. When this method is used, the capacity to form pronephric tubules is determined at the stage of widely open neural folds. (stage 15). The tubular pattern of 2 nephrostomal canals and a common tubule is also determined at this stage. Although, according to this type of transplantation, the determination of tubular pattern occurs in embryos of stage 15, the pronephros acquires its complete determination gradually during the period from stage 15 to the time of the closure of the neural folds, since heterotopic grafts from embryos in these stages never develop completely normal organs. Transplants of partially determined prospective pronephric tissue develop into normal structures in the orthotopic position while they do not do so in heterotopic positions on the flank. This shows that determinative influences are still present in the normal surroundings of embryos in the early tail bud stages.

Tissue from embryos in the late gastrula stage (stage 12) and older has been transplanted into the body cavity of older Ambly-stoma larvae according to the technique described by Holtfreter. 1 Preliminary examination of this material indicates that, according to this method, determination has been acquired by stage 12. If this is substantiated a marked discrepancy will exist between the time at which the pronephros appears to be determined according to the 2 different tests, since, from the standpoint of development there is a wide gap between the gastrula and neurula stages.