220 The Holocephali, or Chimeras 
Relationship of Chimezras.—As to the origin of the Chimeras 
and their relation to the sharks, Dr. Dean has this recent (‘‘ The 
Devonian Lamprey’’) and interesting word: 
“The Holocephali have always been a doubtful group, 
anatomy and paleontology contributing but imperfect evidence 
as to their position in the gnathostome phylum. Their em- 
bryology, however, is still undescribed, except in a brief note 
by T. J. Parker, and it is reasonably looked to to contribute 
evidence as to their line of descent. The problem of the relation- 
ships of the Chimeroids has long been of especial interest to 
me, and it has led me to obtain embryonic material of a Pacific 
species of one of these forms. It may be of interest in this 
connection to state that the embryology of this form gives 
the clearest evidence that the wide separation of the Selachii 
and Holocephali is not tenable. The entire plan of develop- 
ment in Chimera colliet is clearly like that of a shark. The 
ovulation is closely like that of certain of the rays and sharks: 
the eggs are large, the segmentation is distinctly shark-like; 
the circular blastoderm overgrows the yolk in an elasmobranchian 
manner. The early embryos are shark-like; and the later 
ones have, as T. J. Parker has shown, external gills, and I note 
further that these arise, precisely as in shark-embryos, from the 
posterior margin of the gill-bar. <A spiracle also is present. 
A further and most interesting developmental feature is the 
fact that the autostylism in Chimera is purely of secondary 
nature and is at the most of ordinal value. It is found that 
in a larva of Chimera measuring 45 mm. in length, the 
palato-quadrate cartilage is still separated from the skull by 
a wide fissure. This becomes gradually reduced by the con- 
fluence of the palato-quadrate cartilage with the skull, the 
fusion taking place at both the anterior and posterior ends of 
the mesal rim of the cartilage. The remains of the fissure are 
still well marked in the young Chimera, four inches in length; 
and a rudiment of it is present in the adult skull as a passage- 
way for a nerve. Regarding the dentition: it may also be 
noted in the present connection that the growth of the dental 
plates in Chimera suggests distinctly elasmobranchian con- 
ditions. Thus on the roof of the mouth the palatine plates 
are early represented by a series of small more or less conical 
