REMOVAL OF PRONEPHROS OF AMBLYSTOMA 381 
(table 2), twelve had well-formed anterior, and twelve had pos- 
terior nephrostomes. In one instance (PN 2, 17 days) the 
anteror nephrostome had doubled, suggesting the three pro- 
nephric openings normally found in anuran larvae (fig. 14 and 
table 2). 
A study of the development of the mesonephros in operated 
animals will be the subject of further work. 
EFFECT OF REMOVAL OF THE HEART ON THE DEVELOPMENT OF 
THE GLOMERULUS 
In a series of experiments dealing with the effect of removal 
of the heart on certain other organs of the embryo. Doctor Harri- 
son removed the rudiment of the heart in larvae of stages 29 to 
30. Through his kindness, these embryos were made available 
to me for a study of the effect produced on the glomeruli. With 
the incoming of new material (March, 1920), these cases were 
further augmented by additional experiments. 
The glomerulus in Amblystoma punctatum, as has been stated 
in an earher section, normally begins to differentiate from cells 
of the splanchnopleural wall below and at each side of the aorta, 
in stage 36. Within these clusters of cells vacuolated areas 
soon appear, and in a short time connect with the aorta. ^^ 
In embryos from which the heart has been removed before any 
contraction of the cardiac muscles occurred, the initial develop- 
ment of the cell groups is normal. However, as the connection 
with the aorta is established, the more or less compact nature of 
the tufts can no longer be maintained, but from pressure of the 
blood plasma which has collected in and is distending the blood- 
vessels, the vacuolated centers of the glomeruli are torn apart. 
As this accumulation of fluid increases, the outer walls of the 
tufts become more and more flattened, and consequently less 
easily distinguishable from the wall of the aorta, with which 
they are still continuous, finally losing their identity as separate 
organs. It is of interest, however, to note their early formation 
under these circumstances as additional proof of their independ- 
ent power of development. 
1^ A detailed description of this process together with plates is given by Field, 
'91 (pi. 1, figs. 8, 9, 10; pi. 6, figs. 48, 49, 50, 52, etc.). 
