ZOOLOGY: R. B. HOWLAND 
233 
the several organs (retina, lens of eye, digestive tract, etc.) to be in a 
stage of development identical with that in the operated individual. 
On comparison of the models, the evidence of hypertrophy shown in 
microscopic examination was strengthened. The model of the oper- 
ated individual not only showed a considerable increase in length of the 
coiled tubule as contrasted with the control, but by its size indicated a 
great increase in volume. The length of the tubules making up the 
models was determined by taking the average of five measurements. 
The larger model measures 188 cm. (x 200), the smaller model 155 cm. 
,(X 200), showing an increase of 21 per cent over the normal conditions. 
Difference in weight also indicates hypertrophy, the normal model 
weighing 62.9 gr. as contrasted with the larger, which has a weight of 
115.9 gr. 
The formation of the pronephric glomeruli under normal conditions 
as outgrowths from the aorta toward the newly forming kidneys sug- 
gested the possibility that in the operated specimens the glomeruH of one 
side might be lacking. The removal of one pronephros has, however, 
no effect on this development, for in all of the operated embryos both 
glomeruli were present. The glomerulus on the operated side is not as 
uniform in size and shape as the normally functioning one, its form evi- 
dently being largely determined by the width of the coelomic cavity in 
this region. The outer layer of the glomerular capillaries and the epi- 
thelial Kning of the body wall often coalesce. Absence of the pro- 
nephros enlarges the cavity on that side, and the glomerulus is then 
found bridging this cavity as a long strand instead of appearing as a 
more compact tuft of capillaries. 
In the removal of the embryonic pronephros, as much of the tissue was 
scraped out as seemed possible without disturbing the Anlage of the 
aorta. In spite of this fact, a large number of the operated embryos 
possessed well developed anterior and posterior nephrostomes and por- 
tions of the funnels, indicating that these structures are probably re- 
generated from the adjacent coelomic epithelium. Of the sixteen em- 
bryos examined, twelve showed well formed anterior funnels and nine 
had posterior funnels. In one instance the anterior funnel was of a 
pecuKar double form, suggesting the normal condition in those amphibia 
with three pronephric openings. 
The effect of excision of one pronephros on the formation of the seg- 
mental duct on the operated side varied widely. The process of develop- 
ment of the non-functioning ducts is carried on only to a Kmited extent. 
In the embryos examined, every gradation of development was found 
from a condition in which the lumen, though small and flattened dorso- 
