EMBKYOGENY 221 



According to Hackel we can and must come to 

 this conclusion : Immediately upon the monocellular 

 stage of the bird parents there followed organisms 

 which, as hard-shelled eggs with yolk, albumen, etc., 

 swam in the sea or lay upon the sand. These ancestors 

 were absolutely nothing else than such hard-shelled 

 formations. How they acquired the yolk, albumen, 

 and the lime shell, and how they generally worked their 

 way out and, later on, swam as fish in the sea since later 

 they were fish, as the gill rudiment of the bird embryo 

 should prove that is a very difficult question to answer. 1 



It is certain that no Hackelian draws this conclusion. 

 He would rather refer to the saving clause that the 

 ' laws of inheritance [?] and adaptation ' required 

 many things in short, that the krenogenesis must 

 not be left out of account. 



Very probably it would be said that the hard-shelled 

 egg stage which, precisely according to HaekeFs 

 disciples, was certainly not always there but has arisen, 

 may be an adaptation in the embryogeny itself. To the 

 further question In ivhich embryogeny? every one 

 would involuntarily reply : In that of the bird. Any- 

 thing else cannot wisely be put forward, and the sense of 

 the reply is simply this : an actual bird has, in its em- 

 bryogeny, adopted this adaptation, since it no longer, 



1 A particularly logical Hackelian could certainly say with perfect 

 right that it is true that as a rule ' much ' was altered and ' falsified,' 

 but not the lime-shell stage, according to his conviction, since a ' norm,' 

 which could decide the question, is not given. The ' laws of inheritance 

 and adaptation ' also apply and would do so precisely if, generally speaking, 

 no development of the types had taken place. 



