REMOVAL OF PRONEPHROS OF AMBLYSTOMA 
361 
MATERIAL, METHODS AND NORMAL DEVELOPMENT 
Embryos of Amblystoma punctatum were used for all the 
experiments. The stages chosen for operation varied from the 
condition in which the first loop of the pronephric tubules 
appears as a slight, ventrally directed curve of the duct (fig. 1, 
stage 30)^ to that in which the two funnels, together with the 
first loop, appear as a broadened Y (fig. 2, stage 32). In all 
cases embryos were used before contraction of the body muscles 
began, as movement not only hindered the operation, but often 
tore open the wound after successful removal of a kidney. 
PR 
Figs. 1 and 2 Embryos in the stages used for operating. PR, pronephros 
located below the third and fourth myotomes. Figure 1, earliest stage (stage 
30); figure 2, latest stage (stage 32). 
Anaesthetics were unnecessary, and the slight motion due to the 
ciliated epithelium was controlled by holding the animal in the 
field with an operating needle. The body tissues in these early 
stages are easily distinguished from each other through slight 
differences in pigmentation, and, in addition, are so loosely 
bound together as to allow removal of the pronephric mesoderm 
without dislocating the cells of contiguous regions. In a few" 
instances portions of the somatopleural layer ventral to the 
pronephric rudiment were included in the tissue removed, result- 
ing in retarded development, in abnormalities, or even in total 
absence of the limb on this side (Harrison, '18). 
^ See Harrison, R. G., '18, Jour. Exp. Zool., vol. 25, no. 2, p. 417, footnote 9. 
