CIRCULATION IN GASTEROPODA. 211 



The ventricle is oval, and its walls are also thin, although 

 furnished with fleshy columns, crossed in every direction. 

 The aperture between it and the auricle is provided with 

 two valves, which hinder any reflux of blood. The aorta 

 proceeding from the ventricle divides into two trunks ; the 

 first, trending directly to the left, pierces the pericardium, 

 after a very short course, to enter the abdomen ; the second 

 returns at first towards the right, sends off a branch, and 

 then leaves the pericardium also at its right side. The por- 

 tion enclosed in this cavity has attached to it two crests 

 composed of small vessels, which rise from the trunk itself, 

 and again re-enter it, without affording the anatomist any 

 clue whereby to guess the use of such a curious formation. 

 It is always easy to inflate or inject these crests ; and Cuvier 

 hazards a conjecture that they may be secretory organs for 

 the production of the liquid which fills the pericardium. 



But a still more extraordinary peculiarity remains for our 

 notice. The large vessel which carries forward the venous 

 blood to the branchiae, and which may be named either a 

 vena cava or a branchial artery, since it fulfils the functions 

 of both, after sending off arterial branches to the leaflets of 

 the gills, remains for a certain space smooth and entire ; but 

 one part curves itself to the left, and another to the right, 

 and these two branches assume suddenly a new form and 

 structure ; they become, in fact, absolutely confounded with 

 the great general cavity of the body. Their walls are now 

 formed of transverse and oblique muscular ribands, which 

 cross in every direction, but leave between them apertures 

 visible to the naked eye, and permeable to all sorts of in- 

 jection ; thus establishing a free communication between 

 these vessels and the abdominal cavity, so that the fluids 

 contained in the one can readily permeate into the other. 

 This structure is so anomalous, that Cuvier was for some 

 time doubtful of the accuracy of the dissections which 

 seemed to prove it ; but at last he fully satisfied himself, 

 and ascertained distinctly that there was no other vessel 

 to carry the blood to the branchiae except the muscular 

 and perforated cavities just described, and into which all 

 the veins of the body open directly or indirectly. It fol- 

 lows, therefore, that the fluids shed into the abdomen can 

 mix directly with the mass of blood, and be carried to the 

 branchiae with it ; and that the veins perform the office 

 of absorbent vessels. This vast communication, says the 

 great naturalist from whom I borrow these anatomical de- 

 tails, is, doubtless, the first step to that still greater which 

 nature has established in insects, where there is no parti- 



p 2 



