216 MISS M. POOLE ON THE DEVELOPMENT OF THE [ Mar. 2, 
The anterior intermediate air-sacs are at this stage large oval 
vesicles lying in the post-pulmonary septum néar the middle line 
and close against the base of the lungs. The posterior inter- 
mediate air-sacs are much smaller, and enclosed in the extreme 
lateral portions of the same septum. The posterior air-sacs, 
arising from the postero-lateral corners of the lungs, are very 
large and project backwards for a considerable distance into the 
peritoneal cavity. Bertelli says that their posterior ends project 
Text-fig. 28. 
moose 
— noe 
EEA 
= 
oe 
Bia 
Reconstruction, similar to text-fig. 25, of a chick of § days’ incubation. 
beyond the diaphragmatic tissue and thus ‘‘resta libero nella 
cavita addominale tra la parete laterale di questa, il corpo di 
Wolff e Vintestino a sinistra, tra la parete laterale dell’ addome, il 
corpo di Wolff e il fegato a destra.” On this point my own 
observations differ slightly from his. I believe that the posterior 
ends of these air-sacs never extend beyond the hindmost edge of 
the post-pulmonary septum. However far these air-sacs extend 
among the abdominal viscera, they always push before them a 
layer of connective tissue covered with coelomic epithelium. 
Text-fig. 29 is of a reconstruction, similar to text-figs. 25 and 28, 
