382 RUTH B. ROWLAND 
SUMMARY AND CONCLUSIONS 
Fi-om a study of the results obtained after bilateral and uni- 
lateral extirpation of the head kidney and of the heart rudiment 
of Amblystoma larvae, the followinp; conclusions may be drawn: 
1. Conditions ensuing on bilateral removal of the pronephros 
show clearly that this organ is necessary to the life of the embryo, 
although the presence of one pronephros suffices to keep the 
organism alive and in a healthy condition. All embryos from 
which both head kidneys had been extirpated died within from 
eight to twelve days, evidencing during that interval weakened 
heart action, edema, and effusion into the pericardial and abdom- 
inal cavities. Pi-icking the body wall to relieve the edematous 
condition proved ineffective. 
2. Double extirpation does not affect the normal development 
of the glomeruli. These appear in embryos killed four days 
after the operation. 
3. The pronephros remaining after the removal of one head 
kidney takes over the function of excretion usually performed by 
the two organs, and, concomitant with the increased physiolog- 
ical activity, presents marked morphological changes. 
4. The adjustment consequent on unilateral removal consists 
not in the regeneration of the lost part, but in compensatory 
hypertrophy of the remaining organ, a response which has long 
been known to occur in the adult kidney and in other glandular 
organs, both paired and unpaired. 
5. The area of the secreting surface in the hypertrophied 
kidney shows an increase of over 100 per cent when contrasted 
with the normal (2.037 sq. mm.; 1.007 sq. mm.). 
6. The cubic content of the mass of cells constituting the 
hypertrophied kidney as shown by their relative weight is 
increased 63 per cent above the normal. 
7. The length of the tubules shows an increase of 21 per cent. 
8. The number of nuclei in the hypertrophied kidney exceeds 
that of the normal by 16 per cent, due to the occurrence of a 
small amount of hyperplasia. 
9. In single, as well as in double, extirpations, the glomerulus 
develops normally in the absence of the pronephric tubules. 
