6l2 



COMPABATIVE ANATOMY 

 ISr SOMITE SOMrTE 10 



ANTERIOR 

 CAVITy 

 ENDOSTYLE 

 CLUB-SHAPED GLAND 



A. AMPHIOXUS EN/1BRY0 



1ST PERM. GILL-SLIT 



FACIALIS GANGLION PTIC CAPSULE 

 1ST SOMITE 



LENS 



SOMITE 10 



THYROID 

 ST PERM.GILL-SUT 



B. PETROMYZON 



FACIALIS GANGLION 

 1ST SOMITE 



VI 



OTIC CAPSULE 



SOMITE 10 



ANTERIOR CAVITY 



HEART 



C.SQUALUS 



Fig. so6. — Diagrams of the mesodermal segmentation in the head region of chordate 

 embryos. The somites are stippled and nerve ganglia shown in solid black, visceral 

 pouches cross-hatched. A, Larval Amphioxus; B, Petromyzon (cyclostome) ; C, 

 Squalus (elasmobranch) . The neuromeres are numbered with Roman numerals. 



