APP.] SURFACE VIEW. 441 



3. The neural tube : the line of coalescence of the 

 medullary folds, the first cerebral vesicle, the com- 

 mencing optic vesicles, the indications of the 

 second and third cerebral vesicles, the as yet open 

 medullary folds at the tail end. 



4. The heart seen dimly through the neural tube; note 

 its pulsation if present. 



5. The fold of the somatopleure anterior to the heart 

 (generally very faintly shewn). 



6. The fold of the splanchnopleun (more distinctly 

 seen) : the vitelline veins. 



7. The mesoblastic somites. 



8. Indications of the vitelline arteries. 



9. The as yet barely formed tailfold. 



10. The commencing blood-vessels in the pellucid and 

 Tascular areas. 



E. Surface viezv of the transparent embryo from 



below. 



The coverslip must now be removed and the glass 

 slide again immersed in a vessel of clean salt solu- 

 tion. By gently seizing the extreme edge of the 

 opaque area with a pair of forceps, no difficulty will 

 be found in so floating the blastoderm, as to turn it 

 upside down, and thus to replace it on the slide with 

 the under surface uppermost. 



The points which most deserve attention in this 

 view, are : 



1 . The heart : its position, its union with the vitelline 

 veins, its arterial end. 



