228 ON GENERATION. 



circles, and principal parts of the foetus, viz., the liver and 

 heart. He appears to have observed the commencement of the 

 foetus in ovo; but what it was he obviously did not know, when 

 he says, "that the white point in the middle of the circles is 

 the semen of the cock, from which the chick is produced." 



Thus it comes to pass that every one, in adducing reasons for 

 the formation of the chick in ovo, in accordance with precon- 

 ceived opinions, has wandered from the truth. Some will have 

 it that the semen or the blood is the matter whence the chick 

 is engendered; others, that the semen is the agent or efficient 

 cause of its formation. Yet to him who dispassionately views 

 the question is it quite certain that there is no prepared matter 

 present, nor any menstruous blood to be coagulated at the 

 time of intercourse by the semen masculinum, as Aristotle will 

 have it ; neither does the chick originate in the egg from the 

 seed of the male, nor from that of the female, nor from the 

 two commingled. 



EXERCISE THE FIFTEENTH. 



The first examination of the egg ; or of the effect of the first 

 day's incubation upon the egg. 



That we may be the more clearly informed of the effect 

 which the first day's incubation produces upon the egg, we must 

 set out by ascertaining what changes take place in an egg spon- 

 taneously, changes that distinguish a stale egg from one that 

 is new-laid, when what is due to the incubation per se will first 

 be clearly apprehended. 



The space or cavity in the blunt end is present, as we have 

 said, in every egg ; but the staler the egg the larger does this 

 hollow continually grow ; and this is more especially the case 

 when eggs are kept in a warm place, or when the weather is 

 hot ; the effect being due to the exhalation of a certain portion 

 of the thinner albumen, as has been stated in the history of 

 the egg. This cavity, as it increases, extends rather in the line 

 of the length than of the breadth of the egg, and comes finally 

 to be no longer orbicular. 



