M. Souleyet on the Gasteropod Mollusca. 343 



the Bolides and some other closely allied genera*, Cavolina, 

 Tergipes, Calliopcea, Glaucus, &c, genera which often differ 

 only in external characters of little importance, and which cer- 

 tainly form in the class of Gasteropoda one of the most natural 

 families. However, according to the observations of M. de Qua- 

 trefages, these mollusca present in their internal structure the 

 greatest differences : thus the Eolides have a heart and arteries, 

 without a venous system, and in the other genera of the same 

 group which this naturalist examined, there no longer existed any 

 trace of the circulatory apparatus. I have observed Cavolina, 

 Calliopaa, Glaucus, Tergipes (a genus which appears to me to 

 have the nearest relation to the genus Amphorina proposed by 

 M. de Quatrefages), as well as a mollusk which presented the 

 characters assigned by Messrs. Alder and Hancock to their ge- 

 nus Venilia, to which M. de Quatrefages has himself referred his 

 genus Zephyrina, and I can affirm that all these mollusca have a 

 heart and an arterial system, disposed as in the Eolides. It is 

 not very difficult to ascertain the existence of these organs, pro- 

 vided we do not investigate these animals solely as transparent 

 objects. 



I have stated, that even if M. de Quatrefages admits the ex- 

 istence of a heart and arterial system in some of these mollusca, 

 it is not the same with the venous system which he says expli- 

 citly is wanting in all ; and as it was nevertheless necessary to 

 explain, in the Eolides, the return of the blood towards the cir- 

 culatory centre, this naturalist supposes that this fluid, after ha- 

 ving traversed the arteries, is distributed in the general cavity of 

 the body, whence the contractions of the animal propel it in suc- 

 cessive waves to the ventricle. Admitting even this theory as 

 probable, the following anatomical fact, easy of verification in the 

 large species of Eolis, appears to me to destroy it completely. 

 If, after having opened carefully the pericardium, we inject the 

 auricle by the ventricle (an experiment which I have several times 

 performed on the Eolis Cuvierii, common on the coasts of the 

 British Channel) and propel the liquid slowly, we soon see this 



* I do not think we can enumerate among these genera, Eolid'ma, which 

 differ from the Eolides, according to M. de Quatrefages, by the absence of 

 labial tentacles, these tentacles not existing in any of the known species of 

 the genus Eolis. Some authors, from examining individuals contracted by 

 alcohol, have taken for tentacular prolongations, the lateral points formed by 

 the anterior margin of the foot, and have thus assigned three pairs of ten- 

 tacles to these mollusca ; but this error has been already noticed by everal 

 naturalists. 



Some other genera of this group, as Cavolina, Jmphorina, Zephyrina, 

 &c, do not rest equally upon characters sufficiently important or well-ascer- 

 tained for us to adopt them ; but I cannot here enter into a discussion of this 

 subject. 



