THE DRVELOPAfKNT OF LEPIDOSIREN PARADOXA. 



19 



early (except in the middle line and at its outer margin). 

 Where the cells composing the rudiment are in close contact 

 the line of demarcation may be for a time indistinct. But 



inp 



Text-fig. 3. — Section tlirough a complete ciig of stage transverse to axis of 

 embryo, enl. Enteron. m. Mesoblaslic rudiment, m.p. Ectodermal 

 thickening of medullary plate, n. Rudiment of notochord. 



in any case by Stage 14 the mesoblastic rudiment on each 

 side becomes separated definitely from the underlying hypo- 

 blast (except at its outer edge), and a little later (PI. 4, fig. 16, 

 and Text-fig. 3) it becomes separated in a similar way from 

 the axial portion which will give rise to the notochord. 

 This latter remains in the meantime attached to the hypoblast. 

 It should be mentioned incidentally that the cells added 

 to the edge of the mesoderm sheet tend to take on a rounded 



