320 



MOLLUSCS. 



DIAGRAM XVI. 

 Gasteropoda — especially the Snail. 



At the top to the left is a. section of the shell of Helix, showing the 

 columella. 



To the right is a partially dissected Helix (after Vogt and Yung), 

 showing the month {mo. ), the long eye-bearing horns (/. h. ), the short 

 horns { J. h.), the genital aperture (^.), the pulmonary aperture (ap.), 

 the reflected mantle {?».), its vascular wall (p.), the kidney (k.^, the heart 

 ill.), the reproductive organ {rep.) at the top of the visceral spire, the 

 albumen gland {alb. g.), the posterior part of the foot (/). 



Chiton B. shows the eight shell-plates (from Lankester). Chiton A. 

 shows the cerebral ring {/:.), the pedal nerve-cords (/.), the visceral 

 nerve-cords {v.), the sub-lingual ganglia (f. ), (from Lankester, after 

 Hubrecht). 



The reproductive organs of Helix (in part after Vogt and Yung), show 

 the hermaphrodite organ or ovo-testis {herm. organ), the hermaphrodite 

 duct {h. d.), the albumen gland {alb. g.), the female side of the common 

 duct {f. d.), the male side of the common duct (;«. d.), the vas deferens 

 {v. d.\ the flagellum (/.), the penis (/.), its muscle (w/.), the oviduct 

 {ovid.), the mucous glands {m. g.), the receptaculum seminis {r. s.) and 

 its duct, the dart-sac {d. s.), the genital opening {op.). 



At the foot, A represents the incipient trochosphere of Paludina (after 

 Lankester), showing the archenteron {Arc. ) and blastopore {bl. ), B and C 

 (after Gegenbaur) are two forms of veliger, showing foot (/), and 

 velum (f/.). 



