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 

 Lirnapontia, 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, within 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 constriction : 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. 



