THE BIOLOGY OF THE FROG 



CHAP. 



AR 



FlG. 29. Horizontal section through an advanced embryo. AR, archen- 

 teron; BRi.BR*, Z?A', branchial arches; //i, //2, H^, gill slits; HB, 

 hyoid slit ; HM, hyomandibular cleft; JJY, hyoid arch; IN, infundibu- 

 lum ; OF, olfactory pit ; OS, optic stalk ; P, pronephros ; S t segmental 

 duct. (From Morgan, after Marshall.) 



