STRUCTURE AND PHYSIOLOGY OP THE MOLLUSCA. 53 



have a pair of eyes, situated near the labial tentacles (fig. 30*, e\ 

 which are lost at a further stage, or replaced by numerous ru- 

 dimentary organs placed more favourably for vision, on the bor- 

 der of the mantle. 



Most of the aquatic gasteropoda are very minute when 

 hatched, and they enter life under the same form, — that which 



Fig. 30 *. F)y of the Mussel* 



has been already referred to as permanently characteristic of the 

 j)teropoda. (Fig. 60.) 



The Pulmonifera and Cephalopoda produce large eggs, con- 



* Fig. 30*. Fry of mytilus edulis, after Loven. e, eye ; <?', auditory 

 capsule ; / 1, labial tentacles ; s s', the stomach ; b, branchite ; //, heart ; v, 

 vent ; I, Uver ; ;•, renal organ ; a, anterior adductor ; a\ posterior adductor ; 

 /, foot. The aiTows indicate the incurrent and excm-rent openings ; between 

 which the margins of the mantle arc united in the fry. 



