ON GENERATION. 2G9 



At the exclusion from the shell, consequently, certain death 

 hangs over one or other, if not over both. 



Fabricius either not observing the above words of Aristotle, 

 or neglecting them, says : " If an egg have now and then two 

 yelks, it engenders a chick having four legs or wings, and two 

 heads a monster, in short; never two chicks distinct from one 

 another, and that can be spoken of as a pair ; there is but one 

 trunk, to which are appended two heads, &c." 



Whence we may infer that he himself had never seen nor 

 heard from credible persons that such eggs produce two pullets, 

 and therefore that he agrees with me in regarding such eggs as 

 rare, and in holding that they never produce two chicks both 

 alike capable of living. 



I am surprised nevertheless that, with the authority of Aris- 

 totle before him, he should have said that " two chicks, distinct 

 and separate, are never produced from such eggs," but always a 

 monster; the rather as he thinks that the embryo is engen- 

 dered from the chalazse as from the appropriate matter, and he 

 could not but see that there are four chalazse in every twin- 

 egg. 



I should rather imagine that when two vitelli are included 

 by the same albumen in a twin-egg, and are so intimately asso- 

 ciated that their cicatriculse, when they are resolved together, con- 

 stitute a single eye or colliquament, may engender a monstrous 

 embryo with four feet, two heads, &c., because I see nothing to 

 hinder this ; and such a production do I conceive to have been 

 engendered by the egg of which Fabricius speaks. 



But where two yelks have existed separately, parted by their 

 several membranes, and furnished with chalaza?, albumens, and 

 all else requisite to the generation of the chick, I hold that we 

 must conclude, with Aristotle, that such an egg, as it has all 

 the parts of two eggs except the shell, so does it also possess the 

 faculty or faculties of as many; and unless it be a wind or 

 barren egg, that it will for the most part produce two embryos, 

 and but rarely a single monstrous individual. 



