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 XVI 
Vil 
Nin 
Fic. 79. 
Doris pilosa, 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, Nudibranchs, 
