Eeproductive Organs 



34 



Ovo-testis or hermaphrodite gland embedded in liver, consisting of 

 tubes in which ova and spermatozoa are developed. 



The blind end of one of tlie tubes with its contained ova and sper- 

 matozoa shown in fig. 12. 



Duct of ovo-testis. 



Albumen-gland forming an albuminous secretion. 



Vas deferens or duct for conveying spermatozoa, opening into penis. 



Oviduct for conveying ova, ending in vagina. 



Spermatheca or receptaculum serainis (L. receptacle of the semen) 

 opening into vagina. 



Penis with long flagellum (L. a whip), an eversible involution of 



the integument. 



Dart-sac eversible, with pointed dart ) j- l c, ■^ n -i 



_,. , , '■ > peculiar to Siiail family. 



JUucous glands J 



Circulatory System — 



DiAG. 2. Comparative View of Centres of Circulation in — 



a. Worm — Dorsal trunk with transverse vessels discharging into it. 



b. Anodon — Dorsal trunk dilated=the ventricle, and transverse vessels reduced to a pair forming 



the two auricles. 



c. Snail — Dorsal trunk bent upon itself =the ventricle sending blood to anterior end of body by 



cephalic artery, and to posterior end by abdominal artery. Transverse vessels reduced to 



one, the right, forming the auricle. 



Fig. 8. Colourless Corpuscles of the Blood. 



Nervous System and Sense Organs — 



Fig. 9. Nervous System forming a ring round gullet — 



Cerebral or supra-oesophageal ganglia, 



„ , , , !• f Pedal, anterior and united with cerebral by commissures. 



Sub-oesophageal ganglia { „ ' , , . ^ i vi i i i 



( Parieto-splanchnic united with cerebral by commissures. 



Fig. 10. Eyes, a pair, placed at end of tentacles— 



Sclerot'ic (Gr. sHeros, hard) passing into a cuticular cornea. 



Choroid, the j^igmented layer. 



Optic nerve expanding into an outer retina, the fibres of wliich pass through the choroid to form 

 an inner retina with rods and cones nearest the light. 



Vitreous humour (not shown). 



Lens. 



Cornea with a conjunctiva on its outer surface. 

 Fig. 11. Organs of Hearing, a pair close to pedal ganglia — 



Auditory canal. 



Sac containing fluid and otoliths. 



Auditory nerve from cerebral ganglia (not shown). 

 Development — 



DiAG. 3. Early Stages of Development op a Veligerous Gasteropod, no evident velum in Snail — 



Ciliated velum, an expansion of the integument about the head. 



Foot developing, with operculum (L. a lid) upon it. 



Shell external 

 Classification — 



Suh-Kinrjdom — Mollusca. 



NaUtral Order — Odonto'phora, because it has a distinct head ; and an Odontophore. 



Genus — Helix (Gr. a spiral), from the spiral form of the univalve sheLL 



Common Name — Snail 



