198 



ZOOLOGY 



tide, they are stated always to return to it before the water 

 has again receded. 



The visceral hump is covered by the conical shell. The 

 body-wall at its edge is produced into a fold, the mantle. The 

 ventral surface of the animal consists of the muscular oval 



Fig. 118. Diagram of a vertical median section of a Limpet, Patella mdgata. After 

 Lanlsester — Zoological Articles reprinted from the Mncydopcedia Britannica. 



1. Mouth. 10. Heart in pericardium. 



2. Odontophore. 11. Nephridium. 



3. Radula. 12. Opening of larger nephridium. 



4. Radula sac. 13. Branchial efferent vessel (vein). 



5. Buccal cavity. 14. Branchial afferent vessel (artery). 



6. Laminated stomach. 15. Salivary gland. 



7. Intestine cut across. 16. Generative gland. 



8. Liver. 17. Edge of the mantle. 



9. Anus. 



foot, between which and the mantle a groove exists which 

 lodges the gills. The foot is attached to the shell by a 

 circular muscle which is incomplete anteriorly. 



A distinct head exists, and this carries a pair of tentacles 

 with a pair of eyes which appear as black specks near the base 

 of the tentacles. Above the head the groove between the foot 

 and the mantle deepens into a large paUial cavity. Into this, not 

 in the median line, but slightly to the left of it, the anus opens, 

 and on each side of the anus lie the openings of the renal 

 organs (Fig. 119). On the neck are also situated two small 

 bodies representing the ctenidia, which are fully developed in 

 the allied forms Haliotis and Fissurella; in connection with 

 these a patch of olfactory epithelium, the osphradium, has also 

 been discovered. The function of these ctenidia, the original 

 breathing organs, has been assumed by certain folds of the 

 mantle forming the actual gills. 



