MOLLUSKS IN GENERAL 



223 



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

 way. Large octopuses are dangerous antagonists and are feared by 



Pe-^i'ner 



Op-^ic r>e/'\i'e' 



Acjfueoos 



C/llary 

 process 



'"" £p/^he/i'u/r7 



Cornea ( ■f-ransp.) 

 Ins 



WhUe 

 body 



Ccrrf"!! 



OjOfiC nerve 



I Opfic 



nerve> 



y^ (jar7^/i'or> 



Op:f-ic f^erve 



Fig. 128. — Eyes of moUusks. A, eyespot 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 V ergleichende Physiologic der 

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

 much magnified. 



Fig. 129. — 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 M acm.illan 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. 



