Messrs. Hancock and Embleton on the Anatomy 0/ Eolis. 99 



end of the heart ; it is a broad elongated lamina, very thin at its 

 free edge, which is slightly semilunar. It projects a long way into 

 the aorta. Its base is continuous with the fleshy columns of 

 the upper wall of the heart, and just above this connexion, and 

 behind the valve, there is a large well-marked sinus at the com- 

 mencement of the aorta. 



The aorta, fig. 2 d, begins at the base of the valve, and very 

 soon after perforates the pericardium before giving off any 

 branches. 



The elliptical swelling and the transparency observed in the 

 cardiac region during life is mainly owing to the dilated state 

 of the two chambers of the heart. After death the fulness is 

 lost, and the chambers are found contracted and flattened. With 

 some care we have succeeded in a dead specimen in partially in- 

 flating the auricle by means of a small blowpipe, so that the parte 

 resumed a good deal of the appearance they present during life. 

 Fig. 4 represents the chambers of the heart inflated, imitating 

 the condition of the parts during life*. 



In Eolis then we have a simple two-chambered heart, the 

 blood coming from veins into the auricle, passing then into the 

 ventricle, and being thence propelled along the arteries. The 

 pulsations are regular, and their number in E. papillosa is up- 

 wards of fifty, and in E. coronata sixty-five in the minute. The 

 systole of the auricle is followed immediately by that of the ven- 

 tricle, and during the former action the heart is pulled sharply 

 backwards, during the latter forwards, showing the heart to be 

 free in the pericardiac cavity. 



The aorta on emerging from the pericardium gives off a small 

 branch e, for the supply of the stomach, and immediately after- 

 wards bifurcates ; one branch, the larger, passes forward to supply 

 the anterior parts of the body, the other backwards to be distri- 

 buted to the posterior parts. 



* That what we call the auricle is really such, and not a mere sinus or 

 confluence of veins branchio-cardiac, as set forth by M. Milne Edwards in 

 his ' Voyage en Sicile, sixieme article, sur l'appareil circulatoire des The- 

 thys,' we believe for the following reasons. It is distinctly divided from the 

 great venous trunks by the pericardium which is evident enough in Eolis, 

 and strongly defined in Doris: during life, or if injected after death, it pre- 

 sents a well-marked elliptical ampulla within the pericardium, and possesses 

 a pulsation proper to itself, a pulsation that is seen during life to be con- 

 fined within the bounds of the pericardium, and as if in confirmation of this 

 it is found to be furnished with carneae columnae proportioned to the deli- 

 cacy of its coats. 



The branchio-cardiac sinus figured and described by Milne Edwards ap- 

 pears to us to be somewhat anomalous, and certainly differs from anything 

 we have seen either in Eolis or Doris, and is quite at variance with the cor- 

 responding part in the Tritoniadce, of which family it is clearly a member, 

 for in Tritonia Hombergii and in Scyllcea pelagica the auricle is not longi- 

 tudinally, but transversely placed, receiving veins from the skin at each end. 



7* 



