THE GASTRULATION OF AMPHIOXUS. 



T. H. MORGAN and ANNAH PUTNAM HAZEN. 



Material for a study of the process of gastrulation of 

 Amphioxus was collected in 1895 at Faro, Sicily, and at the 

 Stazione Zoologica in Naples. ^ A part of the material was 

 stained at once and surface preparations made ; another part, 

 after staining, was imbedded in paraffine, and the remaining 

 eggs were preserved in alcohol. 



Kowalevski's and Hatschek's account of the gastrulation left 

 many points still unsettled, and Lwoff's description of the proc- 

 ess was so different from those of his predecessors that the 

 entire problem appeared in a new light. Since our work 

 began, no less than three papers have appeared dealing with 

 the gastrulation of Amphioxus. It might seem, under these 

 circumstances, that further work would be superfluous ; yet the 

 more we have studied the process in Amphioxus the more diffi- 

 cult has the problem appeared, and none of these authors seem 

 to us to have reached a satisfactory conclusion. 



Methods. 



The eggs were preserved in several ways. Corrosive-acetic 

 preparations are best for surface views, and show very clearly, 

 both in surface views and in sections, the dividing and the 

 resting nuclei. Hermann's fluid blackens the embryo so that 

 it cannot be used for surface preparations. The y-olk granules 

 come out very clearly in sections, and the cell boundaries are 

 generally very well shown. Flemming's solution — the stronger 

 formula — gives nearly the same results as Hermann's fluid. 

 Embryos fixed by the two latter solutions do not need subse- 

 quent staining, although iron haematoxylin will bring out clearly 

 the nuclei, especially those in process of division. After the 



^ For further details, see Morgan ('96). 

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