BY JAS. P. HILL AND C. J. MARTIN. 
71 
Fig. 4. — Transverse section passing through about the middle region of the 
head plate of mesoderm (hp. mes.). The amnio-cardial vesicles 
(amc. c. v.) form its outer limit. ( x 70.) 
Fig. 5. — Transverse section between the posterior limit of the head plate of 
mesoderm and the auditory plate. The section passes through 
the anterior end of the lateral heart Anlage — the endothelium 
(ht. end.) of which here consists of two tubes. Mesially to the 
heart Anlage the pharyngeal entoderm (ent. ph.) is visible. 
Mesially to the latter the mesoderm is interrupted over a small 
area, (x 70.) 
Fig. 6.— Transverse section through the middle of the lateral heart Anlage. 
The endothelium here forms a single tube, though traces of a 
septum are still visible in it. The (splanchnic) mesodermal wall 
{spl. ) of the heart has here a semitubular shape. The section 
also passes through the 3rd neuromere of the hind-brain (n'".) 
apparent as a thickening of the medullary plate and through the 
grooved auditory plate (mid.). ( x 70.) 
Fig. 7. — Transverse section through the region immediately in front of the 
1st somite. The paraxial mesoderm (mes. ax.) here exists in the 
torm of an arched plate, below which are numerous stellate cells. 
The lateral mesoderm is not completely split, the coelom being 
represented by several interrupted spaces. The median sulcus 
(Riickenfurche) (d. fr.) of the medullary plate is here very 
marked and the notochord is now quite free from the entoderm, 
(x 70.) 
Plate xi. 
Fig. 8. — Transverse section through the 6th somite. The somite somewhat 
oblong in section, is seen to extend mesially below the medullary 
plate and to possess a very distinct cavity (m. s. a). The somite 
is separated from the lateral mesoderm by the Anlage of the 
Wolffian body (w. b. ) Ventrally the latter is distinctly connected 
with the lateral mesoderm, while the connection with the somite 
is not so distinct. The lateral mesoderm splits some distance out 
into a thick somatic layer (som.) and a thin splanchnic layer 
(spi.). The longitudinal strand of cells (le.) immediately 
external to the edge of the medullary plate and passing inwards 
below it is also visible. ( x 70. ) 
Fig. 9. — Transverse section through the 7th somite. In this section the 
Anlage of the Wolffian duct (w. d.) is seen to be distinct from 
the Anlage of the tubule (w. t. ) underlying it. The latter is 
