PHYLUM MOLLUSCA 



747 



primitively right osphradium, which is alone developed, assumes 

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



^^JiiLo^ 



v^st' fyviurr'^ , 



Lcc/n, 



Fig. 638.— Eyes of Gastropoda. A, Fatella; B, Trochus ; C, Turbo; D, Murex. 



tp. epidennis ; /. lens ; op. n. optic nerve ; r. retina ; f. h, vitreous humour. (From the 

 Canibridge Satiiral Histori/, after Helger.) 



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

 termed the parcibranchia 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 

 chambers, which communi- 

 cate internally with the peri- 

 cardium, and open on the 

 exterior, either directly or 

 through a duct — the ureter. 

 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). 



hr.rv 



Fig. 039. — Transverse section of osphradium of 

 Murex. hr. n. branch nerve passing to lamina ; 

 lata. laminsB ; oapkr. n. main osphradial nerve. 

 (After Spengel.) 



