BY JAS. P. HILL AND C. J. MARTIN. 
73 
Fig. 19 (1-9). — Series of transverse sections through the neuromeric region 
of the hind-brain. Sections 2, 4, 6 and 8 pass through the 
neuromeres (n'-n™-), while 1, 3, 5, 7 and 9 show the normal 
thickness of the medullary plate in front of and between the 
neuromeres. ( x 70. ) 
Fig. 20. — Transverse section through the anterior portion of the head 
process of the primitive streak. Three sections in front of the 
internal opening of the blastoporic canal. The lumina (nch. c.) 
in the head process represent the last traces of the chorda-canal, 
(x 340.) 
Fig. 21. --Transverse section through the internal opening of the blastoporic 
canal {bl. op ) into the cavity of the vesicle. ( x 340.) 
Fig. 22. — Transverse section through the head process of the primitive 
streak (h. pr.) - 9 sections behind fig. 21. The blastoporic canal 
is represented by three lumina (bl. c). The head process (h.pr) 
is distinct from the ectoderm, but shows traces of cellular con- 
nection with the entoderm. It is more or less continuous with 
the mesoderm laterally, ("x 340.) 
Fig. 23. — Transverse section through the blastopore (6/.). It opens to one 
side of a longitudinal projection at the front end of the primitive 
groove Ectoderm, mesoderm and entoderm are fused with each 
other in the axial line. ( x 340.) 
Plate xiii. 
Fig. 24. — Transverse section through the anterior end of the primitive 
groove (pr. g.) immediately behind tig. 24. As in that fig. the 
three germinal layers are continuous with each other axially. 
(x 340.) 
Fig. 25. — Transverse section through the united Anlagen of the Wolffian 
duct and tubule in the region of the 7th somite. The Wolffian 
duct Anlage (w. d.) is semilunar in form and is connected at the 
middle of its ventral side with the tubule Anlage (tv. t.). The 
latter possesses a small lumen and is distinct from the somite 
(m. s.), but connected with the lateral mesoderm (mes. I.). 
(x 340.) 
Fig. 26. — Transverse section through the Anlagen of the Wolffian duct and 
tubule some distance behind fig. 25. The Wolffian duct Anlage 
(w. d.) now exists as a flattened band overlying and distinct from 
the rounded tubule Anlage. Its outer edges are closely 
approximated to the ectoderm which immediately over t 
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