380 HOWARD AYERS 
Amphioxus, Ammocoetes, and Bdellostoma, in the order named, 
represent three stages in the phylogenetic development of ver- 
tebrates. They are the only known living representatives of 
the earliest vertebrate forms, as far as our knowledge reaches. 
(4 
Fig. 30 Left side of facial region of skull of Chimaera, to show amphioxine 
jaw apparatus still in existence in a Gnathostome. / to 9 are parts of jaw bar 
and tentacles. 
In view of the great structural differences between Bdellostoma 
and the Chimaeroids and sharks, the extensive changes involved 
in the evolution of the Amphioxine type into the Myxinoid 
type and our incomplete knowledge of both the anatomy and 
embryology of the latter it is evident that additional studies are 
needed if we expect to arrive at satisfactory solutions of the 
