
CERATODUS, PROTOPTERUS, AND CHIM#RA. 503 
lung, the representative of which is absorbed in Chimera. With these changed 
conditions of other organs the heart and the brain have varied concomitantly, without 
our being able to say exactly of what value to the organism the more amphibian brain 
and the more amphibian heart of Protopterus, as compared with those of Chimera, 
may be. 
In figure 13 is given a surface-view of the heart of Chimera monstrosa, as seen from 
the front, the heart being freed from pericardium. The heart has the usual form and 
proportions of that organ in Selachians—an obtuse broad ventricle free at the apex, 
voluminous auricle, and a straight cylindrical cone. 
The ventricle and cone were opened by the removal of a slice not quite sufficiently 
large to bisect these structures. 
The appearance with the slice removed is given in fig. 14. The conus was found to 
be perfectly straight, leading into a relatively much larger ventricular cavity than we 
find in the Dipnoi. In fact there seems little room for doubt that the cavity of the 
ventricle between the auriculo-ventricular valve and the base of the conus, as delineated 
in Chimera, by the change in the character of the walls represents genetically the lower 
vertical and the transverse segments of the arterial cone of Dipnoi. I am inclined to 
think that it is only the upper vertical segment of the cone of Dipnoi which should be 
compared with the outstanding “cone” of the Chimera’s heart. And when these two 
portions are compared in Ceratodus and Chimera the resemblance is found to be exact. 
Chimera (the specimen at least examined by me) has two transverse rows of watch- 
pocket valves in the conus, four in each row, precisely as in the upper limb of my 
specimen of Ceratodus. The agreement extends to the longitudinal pads which exist 
below the uppermost or larger series of valves, but not below the lower and smaller 
row. In fig. 14 only one complete and two cut valves in each row are seen, the rest 
of the wall of the cone and ventricle having been taken away altogther, and not merely 
pinned back (as in the dissections of Ceratodus). 
If, then, we may regard that part of the ventricular cavity to the left in my drawing as 
what in the Dipnoi becomes drawn up out of the heart and developed as an addition to the 
existing cone, we may look in that part of the cavity to the extreme right (the animal’s 
left) for indications of parts corresponding to the auriculo-ventricular curtain valve and 
the basilar fibro-cartilage. I think that it is possible to recognize these in the com- 
ponents of the tricuspid valve by which the auricle and ventricle of the Chimera’s 
heart communicate. 
In order to understand the form of this valve it must be looked at first of all from 
the auricular side ; and it is so seen in fig. 15, A, AVV. A hole like a leech-bite is there 
seen leading from auricle to ventricle. Three pads are placed between the three arms 
of the opening. One of these pads(AVV) is more prominent and membranous than 
the other two. It may be taken to represent the auriculo-ventricular curtain valve of 
Dipnoi. Of the remaining two pieces one is larger and firmer than the other, and 
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