48 



along a line g-oiiip^ obliquely from ri^ht to left (i.e., the 

 long- axis of the ventricle), and re{)resentino' what was 

 the main or antero-posterior axis of the ventricle in 

 ancestral Molluscs. 



On opening this chamber of the heart, the interwoven 

 muscle tihres, which form niucli of its wall, are seen 

 radiating' from the thickened margin of the auriculo- 

 ventricular aperture, which is situated near the middle 

 of its antero-dorsal side. Tlie aperture is guarded by 

 two valvular daps which project into the ventricle cavity. 



The main aorta and its posterior branch, the visceral 

 artery, diverge in opposite directions right from the 

 origin, and as they run parallel to, and in close connection 

 with, the ventricle wall, we get an appearance as of a 

 third chamber of the heart. This appearance is 

 emphasised by the fact that the beginnings of the aorta 

 and visceral artery are swollen, and that this pseudo- 

 chamber resembles the ventricle in general characters. 

 The heart of Patella was described as three-chambered 

 by Wegmann, who gave the name " Intermediate 

 Chamber " to that which is here called " Ventricle," and 

 the name " Ventricle '' to the pseudo-chamber or aortic 

 bulb formed by the swollen arterial bases. AVegmann's 

 determination of pai'ts would make the limpet's heart 

 })ractically i^ui (/ener/s, and woiild remove the genus very 

 far from the Rhipidoglossa, and even from its nearer allies. 

 The present account, on the other hand, shows the essential 

 similarity between Fatel/a and the other Docoglossa in 

 this respect, and agrees with the conclusiojis of ilaller and 

 of Boutan. The aperture between tlie ventricle and the 

 aortic bulb is guarded by a valvular flap which i)rojects 

 into the cavity of the lattei-. 



Arteries. — The Aorta, oi which the oiigin has just 

 lieen described, runs to tlie right end of the pericardium, 



