THE GASTROPODA 



99 



individuals, during normal respiration, the ventricle beats not more 

 than one hundred times nor less than thirty times in a minute. 



XVII 



xv 



XII 



XI 



IV 



VI 



IX 



VIII 



Fio. 79. 



DoritpUosa, opened dorsally. I, stomach ; II, liver ; III, ventricle of heart ; IV, pericardium 

 laid open ; V, pallial vein ; VI, gill ; VII, branchial vein ; VIII, anus ; IX, renal pore ; X, 

 auricle ; XI, reno-pericardial orifice ; XII, posterior part of intestine (the anterior part is on the 

 left) ; XIII, kidney ; XIV, accessory genital glands ; XV, tentacle ; XVI, central nervous 

 system ; XVII, hematic gland ; XVIII, salivary gland ; XIX, oesophagus. (After Hancock.) 



The mean frequency of the pulsations is sixty to the minute in 

 forms most easily observed, such as Pulmonates, Nudibranehs, 



