MEMOIR OF BARON HALLER. 51 



pears, the yolk and intestines are included in the 

 abdominal cavity by means of the acquired irritability 

 of the muscles which cover that cavity, and this 

 animal with a double body becomes a common 

 chicken. So is it in another instance already no- 

 ticed; the heart becomes that well defined organ, 

 instead of being a half ring, separated widely from 

 the spine and placed almost without the chest. It 

 is the cellular membrane, passing from the fluid state 

 to a state of considerable solidity, which draws the 

 separated portions of the heart towards each other, 

 and approximates the whole to the back bone ; and 

 similar causes mould the chick, and bind it upon 

 itself, till it attains that perfection in which we 

 find it. 



" I believe," continues the author, " enough has 

 now been said to vindicate my opinion concerning 

 the doctrine of gradual evolution. The probability 

 appears to be, that all the essential parts of the 

 chick exist throughout all time; not indeed such 

 as they appear in the adult animal, but so disposed 

 that certain and provided causes hastening the in- 

 crease of some of these parts, hindering that of 

 others, changing their relative places, making ma- 

 nifest organs which were formerly transparent, and 

 giving consistence to fluids, in the end form an 

 animal very different from the embryo, but in 

 which no part exists which had not essentially 

 existed before. This is my explanation of develope- 

 ment." 



These observations lead to reflections not less 



