98 THE GASTROPODA 
by haemoglobin in a fairly large number of Streptoneura, ¢.9. 
Littorina, Buccinum, Natica, ete. In some few Gastropods the blood 
is of a bluish tint in consequence of the presence of an albuminoid 
containing copper called haemocyanin. In other cases the blood is 
coloured by pigments of extraneous origin absorbed by the amoe- 
bocytes ; this is the origin of the violet-red colour of the blood of 
Fusciolaria. In various Opisthobranchs, viz. Bullomorpha, Pleuro- 
branchidae, Doridomorpha (Fig. 79, XVII), there is a differentiated 
lymphatic gland, situated as a rule more or less anterior to the 
heart on the aorta. In a certain number of Streptoneura this 
organ consists of a sinus filled with cytogenous connective tissue 
and situated near the kidney ; in other cases it is diffused through 
the subcutaneous connective tissue. 
The heart is always dorsal and in the immediate neighbourhood 
of the respiratory apparatus (Figs. 79 and 82). It is only in the 
very archaic forms such as Pleurotomaria and the Fissurellidae, that 
it is still symmetrical and median as in the Cephalopods, Lamel- 
libranchs, and Amphineura, otherwise it is nearly always lateral, 
being situated on the left in dextral forms (Fig. 67). It is generally 
somewhat anterior in position (Figs. 82 and 88), but it may become 
posterior again as a result of secondary specialisation as in Pterotrachea 
(Fig. 143), Testacella, Oneidiwm, Peronia, and the Doridomorpha, and 
in the last named it resumes an apparent external symmetry 
(Fig. 79). The heart of Gastropods always includes an ovoid or 
piriform ventricle, and in the Rhipidoglossa (with the exception 
of the Helicinidae, Hydrocenidae, and Proserpinidae) two auricles, 
but the latter only retain their primitive symmetry in the Fis- 
surellidae, in which the ctenidia themselves retain their symmetry 
and the heart is median. In other Khipidoglossa, in which the 
heart is no longer median, the right auricle is the smaller (Fig. 
55, VII), and it becomes more and more rudimentary. In all other 
Gastropods there is only one auricle, situated on the topographically 
left side (Fig. 82, aw): it is generally larger than the ventricle, but . 
its muscular fibres are fewer in number and its walls are thin, 
transparent, and extensible. The ventricle is traversed by the 
rectum in the Rhipidoglossa (except the Helicinidae), and in the 
more archaic forms is placed between the two-auricles, e.g. in Pleuro- 
tomaria (Fig. 127, h), Trochus (Fig. 55, VIII), ete. In the majority 
of the Streptoneura (Fig. 99, V), in the Pulmonates (Fig. 86, 
VII), and in some Bullomorpha—e.g. Actaeon, Limacina (Fig. 63), 
Clio virgula, and Clio acicula—this ventricle is posterior to the 
single auricle; in some Opisthobranchs (Phyllirhoé, Fig. 161) and 
Heteropods the auricle and ventricle are on the same transverse 
line, and in the majority of Opisthobranchs (Figs. 79, III, and 
92, I), the Testacellidae, Oncidiidae, Pterotracheidae, and certain 
Calyptraeidae the ventricle is in front of the auricle. In adult 
