378 RUTH B. HOWLAND 
irregularly, and, in general, only to a limited extent. As shown 
in table 2, every gradation occurred, ranging from a condition 
in which the lumen, though small and flattened dorsoventrally, 
appeared throughout the entire length (A 51, 5 days) to a con- 
dition where only the occasional presence of a few degenerating 
cells indicated the location of the atrophied rudiment (Al, 10 
days). 
Fig. 13, PN 2 Showing the increased width of the glomerulus (gl) on the opei- 
ated side. Description in text. X 40. 
Increased activity of a single kidney also has a definite effect 
on the segmental duct of that side. Cross-sections of the duct 
of an individual with unilateral operation, when compared with 
either of the ducts of a normal larva of the same age, show a 
marked increase in diameter. 
Although in the excision of the pronephric rudiment great care 
was taken to remove as much of the somatopleural mesoderm 
as seemed feasible without disturbing the underlying tissues, an 
examination of the operated embryos showed that a large num- 
