Physiology of the Heart. 141 



of the experiments of this investigation. Most of the work 

 was done on the heart in situ, hut the isolated heart was also 

 studied. For the former experiments, the fish was kept on 

 its dorsal surface in a dish of water, the latter reaching suf- 

 ficiently high to cover the gills but not flow over the exposed 

 heart. The respirating centre was left intact. Under these 

 circumstances, the heart may be maintained fairly normal 

 for several hours. 



Considerable differences in physiological behavior have 

 been found in the hearts of fishes, some of which will be 

 noticed under different headings in this synopsis. 



The Structure and Action of the Fish's Heart. In the Sela- 

 chians, as examined by the present writer in the shark and 

 and skate, the heart consists of a Conus arteriosus, in addition 

 to the sinus, auricle and ventricle. This structure is pulsa- 

 tile and seems to be the most sensitive part of the whole 

 heart. 



The corresponding Bulbus arteriosus of other fishes is 

 highly elastic but not pulsatile. 



In observing such a heart as that of Batrachus during 

 systole of the ventricle, the longitudinal and transverse 

 diameters of the latter are seen to be shortened and the 

 antero-posterior lengthened. It is seen that the apex ascends 

 and the bulbus descends. 



In the Selachians, the beat is more highly peristaltic than 

 in the hearts of other fishes, and in the former, a reversal of 

 the order of pulsation for the different parts is most easily 

 originated and maintained. 



In some fishes, as in the eel [Mc William] and Batrachus, 

 there is a part of the heart intermediate between the sinus 

 and the auricle proper, as to appearance, structure, and func- 

 tions ; and, as it is in most respects physiologically like a 

 corresponding part in the Chelonians, has been named by 

 me sinus extension in both fishes and Chelonians ["basal" 

 wall, and " flattened " portion of G-askell, " Canalis Auricu- 

 laris " of Mc William]. This part of the heart is often, under 

 peculiar circumstances, in action when the auricle proper is 

 quiescent, and then serves to conduct the* wave of construc- 

 tion on from the sinus to the ventricle. 



