PLATE 2 
EXPLANATION OF FIGURES 
Median plane reconstructions from sagittal sections of Squalus acanthias. 
The notochord is indicated by cross-barring, the neural plate stippled, entoderm 
and preaxial mesoderm, stippled or black, ectoderm generally in black. All 
figures at the same magnification, X 25. 
17 Series no. 42, no somites, length 1.5 mm. 
18 Series no. 50, 8 somites, length 2.7 mm. 
19 Series no. 52, 11-12 somites, length 2.9 mm. 
20 Series no. 55, 15 somites, length 4.0 mm. 
21 Series no. 56, 16 somites, length ca. 3.0 mm. 
22 Series no. 51, length 4.5 mm. 
23 Series no. 70, 28-380 somites, length ca. 5.0 mm. 
24 Series Gage 3, length 9-10 mm. 
25 Series no. 46, length 9-10 mm. 
26 Series no. 38, length 23 mm. 
F, actual or prospective location of the fovea isthmi and the anterior end of 
the floor plate. 
P, Tuberculum posterius (v. Kupffer). 
I, ‘Tubercle of the floor’ (see text). 
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