442 MALL. [Vov. XII. 
Immediately after this stage there are no embryos in my col- 
lection, so I have no specimen in which the communications 
between the pleural and pericardial cavities are just closing. 
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v 
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Fic. 41. — Diagram to show the Position of the Diaphragm. The numbers on the blocks indicate 
the embryos from which the diaphragms are taken. AO is His’s embryo K O; PP, the out- 
line of the opening between the pleural and peritoneal cavity, which is finally closed when the 
diaphragm reaches the tenth dorsal segment. 
In embryos VIII, V, IX, and XLIII (Figs. 41-43), the pleural 
and pericardial cavities are separated, while the pleural and 
peritoneal still communicate. In the embryos with a vertex- 
breech measurement exceeding 17 mm. the pleural and perito- 
neal have been separated completely. 
