APP.J SURFACE VIEW. 441 



3. The newral 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 Aeosri seen dimly through the neural tube; note 

 its pulsation if present. 



5. The /old of the somatopleure anterior to the heart 

 (generally very faintly shewn). 



6. The fold of the splanchmopleure (more distinctly 

 seen) : the vitelline veins. 



7. The mesoblastic somites. 



8. Indications of the vitelline arteries. 



9. The as yet barely formed tail-fold. 



10. The commenciag blood-vessels in the pellucid and 

 vascular areas. 



E. Surface view of the transparent embryo from 

 below. 



The coverslip must now be removed and the glass 

 slide agaiu 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 iu this 

 view, are : — 

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

 veins, its arterial end. 



