FOURTH PERIOD OF DEVELOPMENT. 139 



He further describes the origin of the notochord 

 plates in a manner not answering to the reality. In 

 common with Max Schultze he regarded them as 

 products separated from the cells. In the notochord 

 foundation which " consists of a distinct notochord 

 sheath and a central part of homogeneous substance ' 

 bodies should make their appearance, these being at 

 first very small and interrupting the light, afterwards 

 coalescing with the notochord plates. 



We shall see that the histological differentiation 

 of the notochord is introduced in a way similar to 

 that usual with vertebrate animals, i.e. by the 

 formation of vacuoles in the cells. The notochord 

 plates constitute the walls of separation which lie 

 between the elongated vacuoles. 



Kowalevsky held the vacuoles, which on their first 

 appearance are very small and round, to be secretions, 

 and later on too confused vacuoles and notochord 

 plates with one another. 



His mistakes are to be referred to his insufficient 

 methods, as well as to the then insufficient views 

 respecting the histological formation of the developed 

 notochord. 



When dealing with the further formation of the 



