498 PROF. RAY LANKESTER ON THE HEARTS OF 
tendency to individual variation in the number and character of the pocket valves of 
the cone of Selachians and Ganoids, he was prepared to find that his two specimens 
differed in the disposition of these parts. In the one there was found an upper row 
of four large watch-pocket valves (close to the origins of the branchial vessels), each 
thickened at its base by a vertical pad, such as Gegenbaur describes in Acanthias ; and 
below this series were observed two papille placed side by side. ‘These Dr. Giinther 
took to be rudimentary indications of a second row of pocket valves. His second spe- 
cimen proved this supposition to be correct; for in it he found the upper row of four 
pocket valves with their pads, and a second complete row of four small pocket valves in 
place of the two papille. 
The specimen examined by me has the valves in this part of the cone more strongly 
developed than was the case even with Dr. Giinther’s second specimen. The upper 
series of four large pocket valves are present, and possess thickened pads which appear 
as the bases of the pockets, not as separated tubercles such as are drawn in Dr. 
Giinther’s plate. The second series of four pocket valves is complete, and the valves 
are relatively larger than in the second specimen figured by Dr. Giinther. It would 
seem possible, from the amount of difference between my specimen and Dr. Giinther’s 
first specimen, that a considerable range of valve-development obtains in the Ceratodus 
cone ; and it is even possible that the delicate valves of the lower vertical segment 
of the cone do not exist, excepting in those specimens which are, so to speak, highly 
valvular. 
The second point is one on which I venture to differ from Dr. Giinther. It appears 
to me that the longitudinal fold in the conus, both of Ceratodus and Protopterus, is 
not to be regarded as consisting of separate parts, viz. valve and muscle, but that the 
whole fold is a muscular contractile ridge which acts as a valve in consequence of the 
spiral disposition of the tube in which it exists. Dr. Giinther, however, describes that 
part of the longitudinal valve which lies in the lower vertical limb of the conus as a 
muscle, whilst only the twisted portion running into the transverse portion of the conus 
is regarded by him as “valve.” Functionally this may be true; morphologically the 
division is, I think, inadmissible. 
The third structural feature to which I will draw attention is the remarkable 
“fibro-cartilaginous mass” first described by Hyrtl in Lepidosiren, which, originating 
in the floor of the ventricle, extends through the auriculo-ventricular passage, expands 
into a large knob in the floor of the auricle, and can then be traced further as a dense 
fibrous ridge right across the floor of the sinu-auricular cavity. 
This structure, and the fact of the complete continuity of “ sinus” and “ auricle,” are 
exhibited in the dissection fig. 4 (FC). A dotted line on the ventricular wall in fig. 3 
indicates the direction of the deep cut which has now been made, the point of the 
scissors being passed completely through the auriculo-ventricular passage. 
Dr. Giinther speaks of the sinus and auricle as distinct structures, the former open- 
