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XXXVI XXXVII XXXVIII 
Fres. XX VII-X XX VIII.—Schematic representations of three stages in the gastrulation of an ascidi 1 
and of an amphibian to show their supposed resemblances in (1) Axial Relations (2) Closure of hese a. eer 
Neural Plate, (4) of Chorda and (5) of Mesoderm. e position assigned to the polar ies in Amphiozus and the amphib- 
ian is to a certain extent hypothetical. The head of the arrow marks approximately the anterior limit of the neural 
plate; the tail of the arrow, the median mesenchyme cells in the posterior (ventral) lip of the blastopore. eso- 
dermal cells or се ы зм cM еч ire жуы : ев 
Gs. - —Right hal sected gastrulae of Cynthia ; the chorda cells are shaded 
the neural plate cells (n. p.) by fine stippl e muscle cells (m.s.) lie lateral to th nc ені (aie) aoa by the 
overgrowth of the anterior (dorsal) lip of the blastopore are separated from the mesenchyme cells anteriorly (X XIX) 
тоя. XX X- XX XII.— Right halves of bisected gastrule of Amphiozus (mainly after Hatschek). In the two earlier 
stages the existence and position of the m erm is hypothetical, being based’ e conditions found in ascidians, 
Ғтав. XXXIII-XXX V.—Right halves of bisected gastrule of the frog (mainly after Kopsch). Тһе areas shaded by 
stippled lines represent the sup i cove y endoderm and yolk, 
Fres. XX XVI-XXXVIII.—Dorsal views of ‘late gastrulæ of ascidian (XXXVI), Amphiozus (XXXVII), and fro 
(XXXVIII). Тһе circles marked 1, 2, 3, 4 indicate successive stages іп the closure of the blastopore. The actual ноен 4 
of the mesoderm іп the ascidian and its sup position in Amphioxus and the frog is shown by the radiating lines 
around the blastopore. The unshaded area (Ch.) anterior to the blastopore and between the halves of the mesoderm rep- 
resents the plate of chorda cells. 
