BTJCCINUM. 317 



well supplied with blood, as will be seen from figure 35. 

 From the afferent branchial vessel a large number of 

 filamental vessels arise which convey the blood through 

 the gills to the efferent branchial vessel. The efferent 

 branchial vessel collects some blood from the mantle 

 which has passed through neither gills nor renal organ, 

 but the quantity is small. Finally it enters the auricle. 



To summarise: — 



1. Blood passes from the ventricle to various parts 

 of the system. 



2. Blood is collected into sinuses and conducted to 

 (a) Renal Organ, and (b) Gills. 



3. The blood passes back to auricle through (a) 

 Renal organ and gills, (b) Renal organ alone, (c) Gills 

 alone, and (d) Mantle alone. 



The largest quantity of blood passes through routes 

 (a) and (b), and that passing by method (d) is almost 

 negligible. 



THE NERVOUS SYSTEM. 



Once more we must emphasise the fact that we are 

 dealing with an example of the most highly developed 

 Prosobranchs. The Nervous System presents the twisted 

 visceral loop characteristic of the Streptoneura, together 

 with extreme concentration of the ganglia. So far 

 as the description of the nervous system is concerned, 

 constant reference has been made to the excellent work of 

 Bouvier on the nervous system of the prosobranch 

 gastropods. All the important details have been worked 

 through again, however, and the figures differ in some 

 minor details from those given in Bouvier's memoir. 



Owing to the extreme concentration which lias taken 

 place, the nerve ganglia may be divided into two groups. 



