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MANUAL OF ZOOLOGY 



In the limpets {Patella and its allies 1 ) (Fig. 179) the 

 true ctenidia are represented only by a pair of vestiges, 

 and respiration is carried on by a number of secondary 

 branchiae (g. I) in the form of lamellae situated between the 

 short lateral fold of the mantle and the foot. In the Pul- 

 monata, and in some members of other groups, ctenidia are 

 absent, and the mantle-cavity, completely enclosed except 



Fig. 179. —Patella VUlgata, seen from the ventral side. /, foot; g. I, circlet of 

 gill lamellae; m. e, edge of the mantle; mit, attachment muscle; si, slits in the 

 attachment muscle; sh, shell; -', efferent branchial vessel; v' , aorta; vc, smaller 

 vessels. (From the Cambridge Natural History.) 



for a small rounded opening, has the function of a pul- 

 monary sac or lung (Fig. 180), its roof being richly sup- 

 plied with blood-vessels; in the aquatic forms its function 

 is apparently as much hydrostatic as respiratory. In some 

 of the Pulmonata there is a return to a completely aquatic 

 mode of respiration accompanied by the development of 



1 Our common eastern American limpet is Acmcea testudinalts. 



