THE EARLY DEVELOPMENT OF SPELERPES 

 BILINEATUS (GREEN) 



HUBERT DANA GOODALE 



ONE PLATE AND SEVENTY-SEVEN TEXT FIGURES^ 



CONTENTS 



Introduction 174 



Part 1. Descriptive 174 



The egg and its envelopes 174 



The egg before cleavage with special reference to the yolk granules 176 



Superficial aspect of cleavage 179 



Regular 179 



Irregular and abnormal 180 



Rate and direction of progress of the third set of furrows 182 



Internal aspect of cleavage 185 



Connected blastomeres 188 



Changes in the size of the egg 189 



Changes in the shape of the blastopore and its fate 190 



Formation and closure of the neural folds 192 



Discussion of the neural groove 194 



Gastrulation 195 



a Descriptive 195 



b Mechanics 198 



c Thinning of the blastula roof 199 



d Origin of the roof of the archenteron 200 



IVIesoderm 202 



Notochord 208 



Neurenteric canal 209 



Part 2. Experimental 209 



Introduction 209 



Method of staining the living egg 210 



Relation between the cleavage planes and the planes of the embryo 212 



The position of the embryo 219 



Eggs marked about the equator 224 



Eggs marked in various places about the blastopore 228 



Amount of advance of dorsal lip 233 



Effects of cold and of salt solutions 234 



Concrescence and convergence 235 



Summary 239 



Literature list 242 



1 Descriptions of figures are given in the text. 



'the AMERICAN JOURNAL OF ANATOMY, VOL. 12, NO. 2 



173 



