XII 



PHYLUM MOLLUSCA 



747 



primitively right osph radium, which is alone developed, assumes 

 the form of a pectinate body with a central ridge, on either side 



f'ff' "i' 1 "//:.. -:w--====^ ,- -- - 







m& 



' /-.->-: : / ' r -i \f, 



op.n -" / ' 



1 A 



B 



r-*& 



43 



' .-I'-/' 



FIG. 638. Eyes of Gastropoda. A, Patella; B, Trochus ; C, Turbo; D, IW 



ty*. epidermis ; 1. lens ; oy>. n. optic nerve ; r. retina ; c. h. vitreous humour. (Fr 

 Cambridge Natural History, after Helger.) 



Murex. 



(From the 



of which is a row of close-set lateral laminae, and is commonly 

 termed the pardbranchia from its resemblance in appearance to 

 a gill. In some cases it is of even more complicated shape than in 

 Triton, owing to the branch- 

 ing of. the lateral ridges. 



The nephridia of the 

 Gastropoda are dorsally 

 placed glandular tubes or 



1 1_ U' 1 



chambers, which communi- 

 cate internally with the peri- 

 cardium, and open on the 



FIG. 639. Transverse section of osphradiutn of 



exterior, either directly O1* Murex. br.n. branch nerve passing to lamina; 



., 11 ,1 / la in. lamin?e ; ospkr. n. main osphradial nerve. 



through a duct- -the ureter. (After Spengei.) 

 Both right and left neph- 

 ridia may be present, though unequal in size, the one situated 

 to the right of the anus being larger than that situated to 

 the left ; or the former may alone be developed (Euthyneura). 



