478 THE ANIMAL KINGDOM. 



anus lies beneath the mantle fold, either on the right side or anteriorly. 

 In Non-Palliata it is sometimes on the right side, but usually in or near 

 the middle dorsal line, as e.g. in Doris. The stomach receives the ducts of 

 the two branched glands known as liver. They are usually large, and 

 often asymmetrical in point of size, especially when the visceral dome is 

 large and spirally twisted. In some Opisthobranchia the liver is repre- 

 sented by a variable number of lobes, which open into a caecum extending 

 backwards from the stomach, or by a number of simple or branched 

 processes originating from the stomach and its single, e.g. Eolis, or double, 

 e.g. Antiopa, caecum. These simple and branched processes extend, one 

 into each of the cerata (infra) in the Eolidia, and in many instances the 

 food passes into them ' as it does in Scorpions ' (Lankester). It is also said 

 that they open at their apices to the exterior, at least in some instances. A 

 caecal gland or * pancreas' is said to exist in some Opisthobranchia^ e.g. 

 Doris, Aplysia, opening into the stomach. An anal gland opens into the 

 anus in Purpura and Murex among Azygobranchia. 



The heart consists of a thick-walled ventricle and thin-walled auricle, 

 the latter receiving the blood from the respiratory organs. The ventricle 

 is pierced by the intestine, and has a double auricle in Haliotis and 

 Fissurella 1 . The ventricle gives origin to an aorta, which soon divides into 

 a cephalic and an intestinal branch. The degree to which these two 

 vessels are developed is very variable. The former may be prolonged to 

 the head, passing between the pedal and pleural ganglia (Natantia, 

 Pulmonatd), and the latter may form a rich network over the intestine and 

 liver, as in the Pidmonata. Eventually the blood passes into the lacunar 

 system of the coelome, but the size of the lacunae is very variable, and in 

 the Pulmonata some of them may have a more or less vessel-like character. 

 The blood passes to and from the respiratory organs in special channels, 

 and the character of the efferent sinuses depends upon the mode in which 

 those organs are disposed, e. g. in many ceratonotous Non-Palliata there is 

 a well-developed longitudinal sinus on each side the body, into which the 

 blood returning from the cerata is collected. The heart is placed some- 

 times in front of, sometimes behind, the base of the ctenidia, and then the 

 auricle lies either anteriorly or posteriorly in the body, with reference to 

 the ventricle. Hence the terms prosobranchiate and opisthobranchiate. 

 The blood consists of a colourless plasma with amoeboid corpuscles. In 

 Planorbis (Pulmonata} the plasma is tinged with haemoglobin, and it con- 

 tains haemocyanin in various Streptoneura, e.g. Haliotis, Fissurella, Turbo, 

 Murex, and in Helix among Pulmonata*. 



1 In Turbo the pericardium is perforated, but not the ventricle ; in Neritina neither. In these 

 two genera and in Nerita the intestine is usually said to pass through the ventricle. Cf. Landsberg, 

 Z. A. v. 1882. 



2 A pericardial gland in the form of lobes upon the auricle occurs in Fissurella, Parmophorus, 

 Haliotis, Turbo, and Trochus, according to Grobben, Z. A. ix. 1886, p. 371. 



