APP.] UNINCUBATED BLASTODERM. 457 



VII. Examination of an unincubated Blastoderm. 



A. Opening the egg. Vide II. A. 



B. Examination of the blastoderm in situ. 



Observe the central white spot and the peripheral 

 more transparent portion of the blastoderm and the 

 halones around it. 



C. Removal of the blastoderm. Vide VI. C. 



With the unincubated blastoderm still greater care 

 is required in removal than with the 20 hours' blasto- 

 derm, and there is no special advantage in doing so 

 unless it is intended to harden it with osmic acid. 



D. Surface view transparent from above. 

 Observe the absence of the central opacity. 



E. Surface view transparent from underneath. 

 Nothing further to be observed than from above. 



F. As an opaque object. 



There is nothing to be learnt from this. 



G. Sections. 

 Manipulation as in VI. G. 

 The sections shew 



a. The distinct epiblast. 



b. The lower layer cells not as yet differentiated 

 into mesoblast and hypoblast. 



c. The thickened edge of the blastoderm. 



d. The segmentation cavity and formative cells. 



