420 MALE, [Vou. XII. 
dorsalis extends to the neurenteric canal, but not beyond it. 
There is no chorda in the tail end of the embryo. 
— 
Sess 
yy 
2 
AY 
gS j hie) 
/ 

Fics. 17-20. — Sections through Embryo No. XII, as indicated by the Lines in Fig. 16. Enlarged 
50 times. The black is the coelom within the body. QO! and 03, first and third occipital muscle 
plates; Cl and C8, first and eighth cervical muscle plates; D!, first dorsal muscle plate ; a, 
aorta; v, omphalomesenteric vein; ¢, thyroid; Z, liver: 4, pharynx ; 2, intestine ; 2 c, neuren- 
teric canal ; #z x, membrana reuniens. 
Throughout the central nervous system, immediately about 
the central canal, there are many karyokinetic figures, showing 
