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 bulk of the bird 

 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, by 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 by the addition 

 of new parts ; but 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 induce ap- 

 pearances which are altogether new. Such is the 

 wrabilical membrane. It is first seen as a soft pulp, 

 then traces of net- work appear in this pulp, pro- 



