AQUEOUS CUKRENT IN THE SPIRACLE OF THE DOGFISH. 91 



signs of pulsation could be seen in the flaps o£ skin (fig. 1) , which conceal the 

 anterior extremities o£ the pectoral fins which can best be seen from below 



If we look a little closer, but still confine our examination to the upper and 

 anterior part of the fish, we can see no sign of movement either in the spiracle 

 or in the mouth, which is slightly open. 



Fig. 3. — Ventral view of tlie postero-lateral angle of the pharyngeal region of Rhina, Avith 

 part of the gill-covers cut away, to show their absolute and relative lengths. (About 

 f nat. size.) 



It is not until we examine the ventral surface of the fish in the mirror that 

 we can see any signs of movement, and even then we find the movement 

 confined to the gill-covers themselves. The movement is expressed on the 

 surface of the first gill-cover, and on as much of the others as can be seen, 

 as a wave passing along it from its fixed anterior to its free posterior edge, 

 and has very much the same appearance as a wave on a field of corn in the 

 wind. There is absolutely no movement of the floor of the pharynx and still 

 less that regular action of the floor which is so characteristic a feature of the 

 living Dogfish, and (though to a less extent) of the Ray. 



The list of differences between Rhina on the one hand, and Scyllium and 

 Raja on the other, is not yet complete. Perhaps the most remarkable feature 

 which distinguishes the Angel from the other fish examined is revealed by 

 the experiments with carmine. Carmine liberated near the spiracle enters it 

 in a uniform stream : that is to say, it is not drawn in rhythmically, as it is 

 in the Dogfish and Hay, at each inspiration. In the case of the adult Angel 

 the stream was perfectly uniform ; in the case of two younger ones there was 

 the faintest trace of pulsation, but this consisted merely in the slightest 

 rhythmical acceleration of the current and not in the alternation of ' current ^ 



