602 PEOF. EAT LANKESTEE ON THE HEAETS OF 



But in the lower segment of the cone of Protopterus, as T have mentioned above, I 

 have found minute pocket valves in the same position as the delicate " ganoid " or 

 pocket valves which I discovered in Ceratodus. The position of these valves is indi- 

 cated at Di; in fig. 11. A magnified view of the valves is given in figure 12. They are 

 so exceedingly small as to be functionally of very little, if any, significance, and may be 

 regarded as evanescent organs. Just as in Ceratodus, so here do we find the under surface 

 of the free margin of the longitudinal spiral valve (fig. 12, Sp v) thrown into transverse 

 folds corresponding with these valves. In fact these folds must be regarded, both in Cera- 

 todus and Protopterus, as indications of pocket valves aiTanged in transverse series on 

 the concave face of the outstanding longitudinal spiral valve. Though so minute, the 

 pocket valves of the conus of the Protopterus heart can be lifted with the point of a 

 fine needle ; and the fact that they are free in front, and attached basally, can be 

 demonstrated. I did not observe chordee tendineee in connexion with these valves, I 

 have as yet only examined two hearts of Protopterus annectens ; and in the better-pre- 

 served specimen I found the valves as figured in fig. 12. In the second specimen I 

 could not detect them, and am inclined to ascribe their absence to the inferior state of 

 conservation of the heart, which was obvious enough. 



III. Heaet op Chim^ea monsteosa. 



The Holocephali are those fish which assuredly come nearest to the Dipnoi of all 

 living forms. The resemblances in some small points are quite striking. Beyond 

 the important points of identity in the structure of the skull and spiral column, 

 we have : — the remarkable scissor-like teeth, closely agreeing in the two forms ; 

 the position of the fold of the nares in Chimwra, and of the anterior and posterior 

 nares in the Dipnoi ; the short oval mass of intestine in both groups, really rendered 

 of considerable length by the close-fitting windings of the spiral chamber within ; the 

 detailed agreement of the urino-genital organs of both sexes respectively ; and, perhaps 

 most strikingly, the identity in Chimcera and the Protopterina of the lines of mucous 

 glands disposed on the head — an agreement the closeness of which was first pointed 

 out by Hyrtl. 



I am not aware that there is any detailed account of the heart of Chimcera or of 

 Callorhynchus extant, and I therefore turned to the examination of a specimen in my 

 possession with considerable interest. The result has been disappointing, so far as the 

 prospect of finding new points of agreement between Chim(era and the Dipnoi is con- 

 cerned. The heart of Chimaera is widely separated from that of Dipnoi, is, in fact, 

 eminently ichthyic and Selachian. The heart is not one of those organs with " a charmed 

 life," the characteristic structure of which remains unaffected by, indifierent to, the 

 immensely important physiological changes passed through on the way fi-om Chimcera 

 to Protopterus. Protopterus, with its raud-lurking habits and air-breathing capacity, 

 has lost, or never developed, the Selachian limb, and has acquired a large functional 



