\I1 



PHYLUM MOLLUSCA 



747 



primitively right osphradium, which is alone developed, assumes 

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



lean 



Ki... 6S8.— Eyes of Gastropoda. A, Patella; li, Trochus ; C, Turbo; I), Blurex. 

 </(. epidermis; '. lens; op. n. optic nerve; ;: retina; c. U. vitreous humour. (From the 

 Caiitbihlgv A'alural History, after Helger.) 



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

 t en ned 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 

 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). 



br.rt. 



Fie. 03i>. — Transverse section of osphradium of 

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

 /«,/*. hnihm; o*phr. n. main osphradial nerve. 

 (After Spengcl.) 



