114 



J. Thos. Patterson. 



as well as in the study of sections (Fig. 43.) Furthermore, Koller 

 ('79 and '81) has figured and described for the unincubated chick 

 blastoderm a thickening in this region. 



Experiment IX. 

 If a very small injury be made on the boundary between the two 

 areas in line with the axis of the future embryo (Fig. XXI,&), it is 



Fig. XX. A photograph of the eiiibiio described iii Experiment VIII. 

 The injured cells are seen at op on' the right neural fold in the region of 

 the open myelon. The primitive streak is bifurcated at the posterior end. 



found later some distance from the posterior end of the embryo (Fig. 

 60, op). Such an operation destroys a considerable portion of the 

 primitive streak material in the region over which it extends (Fig. 

 58), but for twenty-five sections posterior to the injury a normal 

 primitive streak is found. Tlic point of interest in this experiment 

 lies in the question regarding the source of the material from which 

 the tail of the embryo is developed. The material must lie just 

 posterior to the pellucid area, or to either side of the axial line on 



