MEMOIR OF BARON HALLER. 
45 
In the elements of physiology we find the follow- 
ing striking statement : — “ The chick increases very 
quickly ; its length on the twenty-second day is to 
its length on the first day, at least as 1,000,000 to 
1 ; and the whole increase of the hulk of the hird 
during the remainder of its life, does not relatively 
exceed the fifth part of its increase in the egg 
during the first day.” 
And now for his general conclusions I com- 
mence, says he, hy remarking that the animal evi- 
dently undergoes changes solely by the evolution of 
its previously existing parts, without any addition 
of newly created ones. I at one time thought that 
I had found in the heart of the chick the proof of 
the creation of additional parts, and had persuaded 
myself that a curved tube had been converted into 
a muscle with four cavities, simply hy the addition 
of new parts; hut observation has shown me that 
the changes in this important organ are in truth 
only slight, and that they are effected in its pri- 
mordial structure, by successive steps, which are 
the consequences of simple evolution. 
In considering the different ways in which the 
animal which is to form can differ from the animal 
already formed, and how it can assume an appear- 
ance wholly different from what it had, I have 
found that the simple elongation of parts, which is 
naturally produced by the heart, may induoe ap- 
pearances which are altogether new. Such is the 
umbilical membrane. It is first seen as a soft pulp, 
then traces of net-work appear in this pulp, pro- 
