THE GASTROPODA 105 
is permeated by a rich vascular network (Fig. 86) in which the 
blood is oxygenated. In this manner the respiratory pallial 
chamber is transformed into a pulmonary cavity or lung, whose 
vascularised surface is irrigated by the blood derived from various 
parts of the body. The “lung” of Gastropods, then, is not 
a spongy organ, but a cavity 
strictly homologous to the pallial 
cavity. 
The pulmonate Gastropods 
exhibiting this structure are 
polyphyletic, that is to say, 
they belong to several different 
groups. Among the Strepto- 
neura we find three families of 
Via. 85. 
Littorina littorea, male, removed from its 
shell; dorsal aspect ; the mantle-skirt cut along 
its right line of attachment and thrown over to 
the left side of the animal so as to expose the Fia. 86. 
organs of its inner surface. «a, anus; br, : 
ctenidium ; c, heart; h, liver; i, intestine; m.c, Roof of the pallial cavity (lung) of 
columellar muscle (muscular process grasping Limax. Ventral aspect. I, cloacal (reno- 
the shell); p, penis; p.br, osphradium; 7, anal) orifice ; II, pneumostome ; III, reno- 
kidney ; 7’, aperture of the kidney ; ¢, testis; v, pericardial orifice; IV, rectum; V, renal 
stomach ; v.d, vas deferens ; v.d’, the groove-like duct; VI, kidney; VII, heart - ventricle ; 
part of latter; 7, vascular prolongations of the VIII, pericardium (cut open); TX, heart- 
ctenidial leaflets; y, hypobranchial gland. auricle ; X, ramifications of the pulmonary 
(From Lankester, after Souleyet.) vein. (After Leidy.) 
Rhipidoelossa, viz. the Helicinidae, Proserpinidae, and Hydrocenidae ; 
and three sub-groups of Taenioglossa without probosces, viz. the 
Cyclophoridae, Cyclostomatidae, and Aciculidae; and among the 
Euthyneura all the Pulmonates proper, including the aquatic as 
well as the terrestrial forms. In one family only of the Strepto- 
neura, the Ampullariidae, is the ctenidium preserved at the same 
time that a pulmonary cavity is present. In this family the pallial 
cavity is divided by an incomplete septum into a lung and a 
branchial cavity, the former being situated to the left of the 
ctenidium. The animal is therefore able to breathe by its gill 
in the water, and by its lung when out of the water, the air being 
