MOSAIC DEVELOPMENT IN ASCIDIAN EGGS. 



■ BY 



EDWIN G. CONKLIN. 



With 82 Figures. 



I. Normal Development • 146 



II. Objects and Methods of Experiment 151 



III. Results of Experiments 155 



1. Right or Left Half Embryos 157 



a. Cleavage 157 



h. Gastrulation 1 63 



c. Formation of Larva 168 



(i) Neural Plate and Sense Organs 168 



(2) Notochord 1 69 



(3) Muscles and Mesenchyme 169 



2. Three-Quarter Embryos 1 70 



3. Anterior Half Embryos 175 



4. Posterior Half Embryos 179 



5. Quarter Embryos 183 



6. Eighth or Sixteenth Embryos 189 



7. .Anterior and Posterior Half Gastrulec '. 193 



rV'. Other Experimental Work on the ."^scidian Egg 197 



1 . Cleavage 1 98 



2. Gastrula 199 



3. Larva 200 



a. Neural Plate and Sense Organs 203 



h. Notochord 204 



c. Muscles and Mesenchyme 205 



V. Regulation in Ascidian Egg and Embryo 206 



VI. General Conclusions 209 



1. Organ-Forming Substances 209 



2. Localization of Oijplasmic Substances 210 



3. Cleavage and Localization 213 



4. Determinate and Indeterminate Cleavage and Development 214 



Summary ■• 216 



Literature Cited 221 



In almost every instance in which fragments of eggs or isolated 

 blastomeres have been found to be capable of giving rise to entire 

 larvae the substance of the unsegmented egg is apparently undiffer- 

 entiated and the cleavage cells are so nearly equal and homo- 

 geneous that it has not been possible to trace the lineage of individ- 



