O.'T 7 1901 



The Development of Lepidosiren paradoxa. 



Part II. 



With a Note upon the Corresponding Stages in the Development 

 of Protopterus annectens. 



By 

 J. Orahaiii Kerr. 



Willi Plates 1—4. 



Contents. 



PAGE 



Introduclion ........ 1 



Methods ........ 3 



Early Stages in Devclopriiciit, : 



JSegnienlation and Origin of Segmentation Cavity . . 6 



Gastrulation ...... 10 



Tate of the Segmentation Cavity . . . .16 



Origin of Mesoblast and Notocliord . . .17 



Origin of Coeloni ...... 20 



Early Development of Notochord . . . .20 



Origin of Central Nervous System . . . .22 



Note upon the Early Development of Protopterus . . 23 



Note upon Size of Nuclei in Lepidosiren Egg . . .25 



General Remarks upon the Phenomena described . . .25 



Summary of Facts ....... 37 



Explanation of Plates ....... 38 



Intkoduction. 



The following pages constitute a further instalment of my 

 description of the developmental phenomena of Lepido- 

 siren paradoxa.^ I have devoted much time and 



' The first instalment, containing a description of the "External Features 

 in Development," is to be found in ' Phil. Trans. Roy. Soc.,' B, vol. cxoii, p. 

 VOL. 45, PART 1. NEW SERIES. A 



