FURTHER STUDIES ON THE GERMINAL LAYERS ETC. 49 



lateral plates split off from the hypoblast, and that the notochord 

 originates as a median plate, siniultancously witli the mesoblast. with 

 which it may sometimes be at first continuous." (loc. cil. }). 157. 

 edition of l(S8.">j. Now suppose that the earlier phases of the meso- 

 blast formation in Chelonia are ^ery rapidly gone through or al- 

 together skipj)ed over, and the state represented in Figs. 17 and 38 is 

 venchaà per saltum : we shall then necessarily obtain appearances which 

 would make us conclude that the lateral plates of the mesoblast, 

 or at least the part of it immediately adjacent to the chorda, becomes 

 split off from thé hypoblast. My contention then is that the process 

 of the mesoblast formation in the chick is an extremely abbreviated 

 form of the ])rocess descril)ed above in Ciemniys or Trionyx . The 

 question naturally arises whether cells are added on to the mesoblast 

 from the gut-liypoblast, outside of the .tretch of epithelium represent- 

 ing the walls of the gut-diverticulum. I wish to leave this question 

 open at present : there are ap})earances which lead me to think so, but 

 the}' are by no means conclusive. Theoretically, there should be no 

 cells added outside of the gut-diverticuJum. 



Science College, June, 1891. 



Contributions to the Embryology of Reptilia. 



(No. 1. ) I. Uu the Formation of the Germinal Layera in Chelonia. Quart. Jour. 



Micr. !Sc., Vol. 27. Also reprinted in Jour. 8c. College, Tokyo, 



Vol. I, pt. 3, 

 (No. 2.) II. On the Foetal Membranes of Chelonia. Jour. tSc. College, Tokyo. 



Vol. IV., pt. 1, 



