LEPIDOSIliEN PARADOXA. 
79 
AVith tlie fusion of the mesoderm below the ventral 
surface of the pharynx and the formation of the bilateral 
Text-fig. 6. 
A. 
A. Section transverse to the heart-riidiment at Stage 24, b. Sec- 
tion transverse to the heart, showing endothelial rudiments of 
the paired ventral aortae. my. Myocardium, per. Outer wall 
of pericardiac cavity, pli. Pharyngeal rudiment, v. a. Rudiment 
of the paired ventral aorta3. v. c. Vessel-cells with unexpanded 
cardiac cells between them. y. Yolk. 
pericardiac coelom, the two endothelial strands meet on the 
anterior surface of the yolk, and form a little single-layered 
sheet of endothelial cells forming the rudiment of the heart 
(Stage 24, Text-fig. 6 a, v. c.). 
This fusion of the mesoderm below the pharynx occurs 
