MOLLUSKS IN GENERAL 



227 



cavity and siphon resemble those of the squid and are used in a similar 

 way. Large octopuses are dangerous antagonists and are feared by 



Acjueous 



Cornea (-f-rcrnsp,) 



C/'/!ar/ 

 process 



■/■he/i'urr7 



Opfic 

 ner\/e 



Whiie 

 body 



(Tar-f'/ /ct^t 



(JarT^/n 

 Op'f/'c r?erve 



Optic /lerve 



Fig. 137. — Eyes of mollusks. A, eye spot of Patella, a gastropod, possessing only an area 

 of pigmented epithelium, or retina, and optic nerve. B, the eye of Murex, another gastro- 

 pod, showing a well-developed eye with lens, retina, and optic nerve. {From Cooke, 

 "Cambridge Natural History," after Hilger, by the courtesy of The Macmillan Company.) 

 C, diagrammatic section of the eye of a cuttle fish. Sepia sp., showing many parts analo- 

 gous to the eye of a vertebrate. (From Jordan, " Allgemeine Vergleichende Physiologic der 

 Tiere," after Hensen, by the courtesy of Walter de Gruyter & Company.) All figures 

 much magnified. 



Fig. 138. — An octopus. Polypus bimaculatus (Verrill). A small specimen drawn from 

 life. {From, Johnson and Snook, "Seashore Animals of the Pacific Coast," by the courtesy 

 of The Macmillan Company.) 



divers, for if they get hold of a person under water struggling merely 

 causes them to cling the tighter, and release can be secured only by chop- 

 ping the tentacles from the body. 



