CASTLE. — CELL LINEAGE OF THE ASCIDIAN EGG. 213 



has recognized between the early stages of Ciona and those of Clave- 

 liua renders its occurrence in Claveliua exceedingly improbable. 



Davidoff's belief that the first equatorial cleavage separated the two 

 primary germ layers can have no weight une way or the other in de- 

 ciding the (juestion, for Davidoff did not profess to have traced cell 

 by cell the history of the cleavage subsequent to the 8-cell stage. 



If my statements in this Postscript seem to the reader to be as dog- 

 matic as Samassa's, I can only say that they rest, not on confessed 

 inference or conjecture as to the cell lineage, but on repeated observa- 

 tions made on dozens of embryos, only continuous observations of the 

 living egg or the presence of karyokinetic figures in preserved speci- 

 mens being admitted as sufficient evidence of the genetic relationships 

 of cells. The evidence afforded by my figures will be presented, and 

 a more exhaustive discussion of the subject made, in a subsequent 

 paper. 



October 5, 1894. 



LITERATURE CITED. 



Chabry, L 



'87. Contribution k rembryogenie normale et teratologique des 

 Ascidies simples. Journ. Anat. et Physiol., Tom. XXII. pp. 167- 



319, PI. xvm.-xxii. 



Davidoff. M. v. 



'89-'91 Untersuchungen zur Entwickiungsgeschichte der Distaplia 

 magnilarva, Delia Valle, einer zusammengesetzten Ascidie. Mitth. 

 Zool. Stat. Neapel, Bd. IX. Theil I. pp. 115-178, Taf. V., VI., 

 und Theil 11. pp. 533-651, Taf. XVIII.-XXIV. 



Kofoid, C A. 



'94. On some Laws of Cleavage in Limax. Proc. Amer. Acad., Vol. 

 XXIX. pp. 180-200, 2 Pis. 



Seeliger, O 



'85. Die Entwickiungsgeschichte der socialen Ascidien. Jena. Zeit- 

 schr , Bd. XVIII. pp 45-120, Taf. I.-VIII. 



Van Beneden, Ed., et Julin, Ch. 



'84. La segmentation chez les Ascidien et ses rapports avec I'or- 



ganisation de la larve. Arch, de Biol., Tom. V. pp 111-126, Pi. 



VII., VIII. 

 '86. Recherches sur la morphologie des Tuniciers. Arch, de Biol., 



Tom. VI. pp. 237-476, PI. VII.-XVL 



