THE LOWER VBRTEBRATA. 



195 



laying it open from the ventral side in the region in 

 front of the atriopore (fig. 103), we find a cavity which at 



Kg. 104. TRANSVERSE SECTION OF AMPHIOXUS m PHARTNGRAL REQIOH. 



(DicOgrammatic ; combined from figures by Boveri and others.) On the left side 

 a ^ill-arch, nephridium, gonad, and ventral nerve ; on the right a gill-slit 

 and dorsal nerve. 



first sight may be taken for the coelom. 

 cavity lies the pharynx, with its pill -slits, 



But in this 

 gill-slits do 



