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 



FIG. 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 

 organs of its inner surface. , anus ; br, 

 ctenidinin ; c, heart ; h, liver ; i, intestine ; m.c, 

 columellar muscle (muscular process grasping 

 the shell) ; p, penis ; p.fer, osphradium ; r, 

 kidney ; r', aperture of the kidney ; t, tostis ; r, 

 stomach; v.d, vas deferens ; v.d', the groove-like 

 part of latter ; x, vascular prolongations of the 

 ctenidial leaflets ; y, hypobranchial gland. 

 (From Lankester, after Souleyet.) 



Fio. 80. 



Roof of the pallial cavity (lung) of 

 Limiac. Ventral aspect. I, cloacal (reno- 

 anal) orifice ; II, pneumostome ; III, reno- 

 pericardial orifice ; IV, rectum ; V, renal 

 duct; VI, kidney; VII, heart - ventricle ; 

 VIII, pericardium (cut open); IX, heart- 

 auricle ; X, ramifications of the pulmonary 

 vein. (After Leidy.) 



Rhipidoglossa, 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, %nd by its lung when out of the water, the air being 



