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 



IX 



Fio. 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, n, anus ; br, 

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

 columellar muscle (muscular process grasping 

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

 kidney ; r 1 , aperture of the kidney ; t, testis ; v, 

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

 part of latter; x, vascular prolongations of the 

 ctenidial leaflets ; y, hypobraucliial gland. 

 (From Lankester, after Souleyet.) 



Fio. SO. 



Roof of the pallial cavity (lung) of 

 Umax. 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, and by its lung when out of the water, the air being 



