124 
embryo of Bdellostoma gives no evidence that any structures directly 
comparable to visceral arches occur at any stage. The various skeletal 
elements which occur in late embryos in the hinder region of the 
head have probably arisen as neomorphs in especial relation to the 
muscles of the barbels and tongue. These elements certainly do not 
appear until after the gill-slits have passed entirely out of their 
neighbourhood’’,') and CoLE makes the remark, with reference to these 
same cartilages, that he is “disposed to believe that much of the 
Myxinoid skeleton is recent and sesamoidal (as indicated by PoLLARD), 
and therefore has no morphology at all”. In Petromyzontes the 
branchial skeleton is formed by the union of at-first-separate small 
skeleton bars lying external to the branchial vessels (SmirLEyY 36, 
NEUMAYER?)) and apparently in much the same position as the extra- 
branchial cartilages of Elasmobranchs, but in view of the fact that these 
extra-branchial cartilages are merely peripheral cvalesced portions of 
the gill-rays which have become segmented off (Footr 9a), there is 
no reason for supposing that any genetic homology exists between 
the two sets of structures. Briefly stated, the whole subject of the 
comparison of the branchial and facial skeletons in Marsipobranchs 
and Gnathostomes comes to this: if Marsipobranchs have originated 
from a Gnathostomatous stock, then it is wholly inexplicable that in 
this group the two interior visceral and posterior branchial arches 
should exhibit the differences in development (in time and form) and 
relationships to nerves, muscles and blood-vessels that the sub-ocular 
arch, piston, styloid, branchial basket and other cartilages do when 
compared with the jaw and hyoid arches and branchial bars of 
Gnathostomes. If ancestral Marsipobranch possessed jaws, they were 
not the jaws of existing Gnathostomes but rather cirrhostomial struc- 
tures, such as those described by PoLuarp (29, 30), but to assume 
this is to adopt Batrour’s contention. 
(E) In the British Association Report of my discussion (38) on 
this subject I have stated that “it is difficult to conceive a gnatho- 
stomatous Craniote using its mouth for attaching itself to a foreign 
object without employing its jaws in so doing. Jaws are ipso facto 
organs of seizing and it is incredible that any animal which had once 
acquired this habit should substitute its “lips” for its jaws when 
1) My italics. 
2) I have not had an opportunity of consulting NEUMAYER’'S papers. 
