of Gasteropodous Mollusca. 413 
together on the superior wall near to the channel of the great 
mucous gland^ and then communicate with each other. Hence 
the inference that the eggs may possibly receive the fertilizing 
influence of two individuals, as we suppose to be the case with 
the Nudibranchs. The most interesting modification of these 
organs is in the position of the external orifices. In Eolis all these 
three are placed close together within a common opening : in 
Limapontia, as before described, the orifice leading to the sper- 
matheca is removed to a considerable distance from the other 
two. The nature of these orifices becomes therefore better under- 
stood. From this arrangement we have been enabled to deter- 
mine beyond a doubt, that the channel leading to the sperma- 
theca is really the copulatory channel, and that the orifice at the 
base of the penis is that through which the eggs pass ; and thus 
the anatomy of this animal becomes confirmatory of our views, 
elsewhere expressed, of these parts in Eolis-. 
Vascular and Respiratory Systems . — From the minuteness of 
the species on which our observations were made, we have not been 
able to trace the former system to any great extent. The heart, 
however, we have determined with sufficient precision : it is com- 
posed of two distinct chambers, — a ventricle and an auricle. 
These may be seen by placing the animal sideways in the com- 
pressor. We succeeded in this way, after having made several 
fruitless attempts in the usual manner, of depressing the animal 
with the back uppermost. In the more transparent individuals 
the heart may be observed beating near the middle of the back, 
within an indistinct, irregular, oval swelling, without the aid of 
the compressor ; but the best way of ascertaining its parts is that, 
above-mentioned, of compressing the animal sideways, and thus 
obtaining a profile view of the heart. In this position the two 
chambers are rendered quite obvious. They lie immediately be- 
low the skin, wfithin a clear space, which perhaps indicates the 
extent of a pericardium. The ventricle is placed in advance of 
the auricle, and is pyriform, with the apex in front ; the auricle 
is a little larger than the ventricle, and is separated from it by a 
very marked eonstriction : its form resembles that of the ventricle, 
but is a little narrower and has the attenuated end posterior ; 
this end terminates in a well-defined vascular trunk, which ap- 
pears in close contact with the skin. By adjusting the pressure 
so that, when the parts are rendered sufficiently transparent, the 
heart is permitted to swell and contract, the blood may be seen 
passing along the aorta, which issues from the anterior apex of 
the ventricle. In this way we could trace the aorta as far as the 
buccal mass, where it bifurcates. On leaving the ventricle it dips 
a little downwards, and then advances towards its destination. 
