BREATHING ORGANS IN PROSOBRANCHIATA 



157 



which included Patella and Chiton^ has no value, and has indeed 

 long been discarded. In Cliiton the gills never extend completely 

 round the animal, but are always more or less interrupted at 

 the head and anus. They are the true gills, the plumes being 

 serially repeated in the same way as the shell plates. 



Fig. 63. — Patella vulgata L., seen from the 

 ventral side:/, foot; g.l, circlet of gill 

 lamellae; m.e, edge of the mantle; mu, 

 attachment muscle ; 6-/, slits in the same ; 

 sh, shell ; v, vessel carrying aerated blood 

 to the heart ; v ' , vessel carrying blood from 

 the heart; ve, small accessory vessels. 



Fig, 64. — Patella vulgata L., seen from 

 the dorsal side after the removal of the 

 shell and the black pigment covering 

 the integument ; the anterior portion of 

 the mantle is cut away or turned back : 

 a, anus ; 6r, hr, remains of the true 

 branchiae (cteuidia) ; z, intestine; k,k', 

 kidneys; k.ap, their apertures on each 

 side of the anus ; I, liver ; m, m, mantle ; 

 mu, attachment muscles, severed in re- 

 moval of shell; t, t, tentacles. 



In the land Prosobranchiata (Cyclostomatidae, Cyclophoridae, 

 Aciculidae, Helicinidae) which, having exchanged a marine for 

 an aerial life, breathe air instead of water, the branchia has 

 completely disappeared, and breathing is conducted, as in the 

 Pulmonata, by a lung-cavity. In certain genera of land oper- 

 culates, e.g. Piipina^ Oataulus^ Pterocyclus^ a slight fissure or tube 

 in the last whorl (see Fig. 180, p. 266) serves to introduce air 

 into the shell, which is perhaps otherwise closed to air by the oper- 

 culum. In Aulopoma^ which has no tube, the operculum admits 

 free circulation of air. In certain other Cyclostomatidae the 

 apex is truncated, and air can enter there. De Folin closed 

 with wax the aperture of Cycl. elegans^ and found that on plac- 

 ing it in a pneumatic machine, the shell gave off air through its 



