We explored intraspecific variation in vertebral formulae, more specifically the variation in the number of thoracic vertebrae and frequencies of transitional sacral vertebrae in Triturus newts (Caudata: Salamandridae). Within salamandrid salamanders this monophyletic group shows the highest disparity in the number of thoracic vertebrae and considerable intraspecific variation in the number of ...

C E L L movement and migration seem to play an important role in the formation of tissue-patterns during embryogenesis. Phenomena such as the appearance of loosely attached cells in the mesoderm, or of the freely migrating neural crest cells, are quite common in embryonic development. Since the tissues of adult organs are mostly rather compact in structure it seems that the capacity of isolated...

The flicker response curve for the newt Triturus viridescens (water phase) has much the same quantitative structure as that found with various fresh-water teleosts at the same temperature (21.5 degrees ). The variability of critical intensity and of critical flash frequency likewise follows the same rules. The cone portion of the F - log I curve is much more widely spread, however. This, and th...

Newt oocytes were dissected under liquid paraffin and known volumes of clean nucleoplasm and cytoplasm were obtained from oocytes in different stages of oogenesis. The samples were digested in redistilled nitric acid, diluted with deionized water, and their Na and K contents were measured by flame spectrophotometry. The results were expressed as micro-equivalents of Na and K per millilitre of n...

The membrane potential in the blastomeres of dividing Triturus egg cells increases progressively from the first cleavage to the late morula stages. Both the animal and vegetal poles show the same increasing trend in potential; there is no significant potential difference between them. Upon first cell cleavage, the total resistance of the egg cell surface in contact with the exterior decreases t...

proportions proceeds differentially in the first or in the second and third dimensions. 1 Castle, W. E., Proc. Nat. Acad. Sci., 10, 19-22 and 181-182 (1924). 2 Sumner, F. B., Ibid., 10, 178-180 (1924). Castle, W. E., Carnegie Inst. Pubi., No. 320 (1922). 'Cohen, J. I., Nature, 144 944 (1939). Cohen, J. I., J. Mental Science, 86, No. 362 (1940). 6 Pearl, R., Constitution and Health, London, Kega...