IV. i INITIAL STRUCTURE OF THE GERM 



239 



posterior portion of a young Ascidian will regenerate a new head 

 with pharynx and eyes ; the anterior half dies. 



Driesch has also maintained that the isolated blastomeres 

 (f> f> i) of the same species give rise ultimately to total 

 gastrulae and these to larvae. The larvae are, however, unable to 

 hatch out and are defective with rudimentary eyes, otolith and 

 suckers or devoid of these organs altogether. 



FIG. HI. Cynthia partita. Posterior half embryos. (After Conklin.) 

 a, 32-cell stage, dorsal view. Cleavage is quite normal, b, 76-cell 

 stage, dorsal view. Muscle-cells (B 8.8, B 8.7 and B 7.8) and posterior 

 mesenchyme cells (B8.6, B 8.5, B 7.7, and B 6.3) and posterior endoderm 

 cells (B 7.1, B 7.2) are seen, c, later stage, deep focus, showing ventral 

 endoderm (v end.) with a mesenchyme (m'ch.) on each side, d, same 

 stage as last, showing muscle-cells (ms.). 



LITERATURE 



L. CHABKY. Contribution a Pembryologie normale et teratologique 

 des Ascidies simples, Journ. de I'Anat. et de la Phys. xxiii, 1887. 



E. G. CONKLIN. The organization and cell-lineage of the Ascidian 

 egg, Journ. Acad. Nat. Sci. Philadelphia, xiii, 1905. 



