THIRD PERIOD OF DEVELOPMENT. 101 



compose this notochord foundation, he gives no infor- 

 mation here, and mentions too nothing with respect 

 to the relation of these matters to his earlier state- 

 ments. 



In material points I can confirm his statements ; 

 I will however mention that the middle fold of the 

 hypoblast is not entirely expended on the formation 

 of the notochord, but that its side cells form the 

 dorsal portions of the alimentary canal. The noto- 

 chord, too, at the time when Kowalevsky represents 

 it as completely split from the membrane of the 

 archenteron, is still in continuous connexion with it. 

 And even, in later stages, when it has already attained 

 to its separation, it still for some time takes part in 

 forming the wall of the alimentary canal. Further 

 differences, which I do not intend to describe more 

 closely here, may be gathered from a comparison of the 

 figures. 



I will now proceed to give an exhaustive description 

 of my own observations. 



In the living object the first processes of the noto- 

 chord formation are not to be followed very exactly. 

 It may be seen, indeed, that a strand is marked off 

 dorsally from the archenteron in the neighbourhood 



