QUANTITATIVE ANALYSIS OF NORMAL GROWTH OF THE PRONEPHRIC SYSTEM IN LARVAL AMPHIBIA

The pronephric systems of young larvae of Ambystoma mexicanum, Hynobius nebulosus, Cryptobranchus japonicus and Rana esculenta were quantitatively analysed and compared with each other and with previous data of Neoceratodus. The morphological arrangement of the nephrostomial units was described. Cryptobranchus had the largest pronephric system among the urodeles. In terms of total larval length a comparison of the regression lines of a variety of pronephric components showed some of them to grow faster in Cryptobranchus than in axolotl, but the slopes of the regression lines of all components of Hynobius were not significantly different from those in axolotl. In all genera within the range of development studied the pronephric nuclear population, total pronephric tissue volume and overall pronephric volume increase with increase of larval length except in Rana , where the latter component measurement is stable from 17 mm. onwards. Glomus volumes and glomus external surface areas, except those for Neoceratodus , continue to enlarge. The pronephric cell volume size range is of a similar order in all genera except in Cryptobranchus larvae from 26 mm. to 32 mm. in length where it is considerably higher.