It is absent in the most primitive and symmetrical forms, such as Haliotis and Pleurotomaria.
17, d), we find right and left of the two renal apertures a right and left gillplume or ctenidium, which here as in Haliotis and Pleurotornaria retain their original paired condition.
The heart in Patella consists of a single auricle (not two as in Haliotis and Fissurella) and a ventricle; the former receives the blood from the branchial vein, the latter distributes it through a large aorta which soon leads into irregular blood-lacunae.
9, 10) of _ the nervous systems of ` Patella and of Haliotis, e as determined by Spengel, show the identity in the origin of the nerves passing from the visceral loop to Spengel's olfactory ganglion of the fig..
Limpet, and that of the g ' nerves which pass from the visceral loop of Haliotis to the olfactory patch or osphradium, which lies in immediate relation on the right and on the left side to the right and left gill-plumes (ctenidia) respectively.