Messrs. Hancock and Embleton on the Anatomy o/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 ofi* 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 parts 
resumed a good deal of the appearance they present during life. 
Eig. 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 hranchio-cardiac, as set forth by M. Milne Edwards in 
his ‘Voyage en Sicile, sixieme article, sur I'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 carneag columnse 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, hut transversely placed, receiving veins from the skin at each end. 
7 * 
