STRUCTURE AND PHYSIOLOGY OF 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 



h 



yV 



Fig. 30*. Inj of the Mussel'' 



has been already referred to as permanently characteristic of the 

 ^teropoda. (Tig. 60.) 



The Pulmonifera and Cephalopoda produce large eggs, con- 



* Fig. 30*. Fry of mytihis edulis, after Loven. e, eye; e', auditory 

 capsule ; 1 1, labial tentacles ; s s', the stomach ; b, branchi?e ; h, heart ; v, 

 vent; I, liver; r, renal organ; a, anterior adductor; aV posterior adductor; 

 /, foot. The arrows indicate the incurrent and excurrent openings ; between 

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



