THE EVOLUTION OF THE EYE. 87 



Semper gives this only as an hypothesis, because the globules, 

 being microscopically small, could not be seen by him to fly in 

 showers. But what is certain is that Onchidium has these dorsal 

 eyes of vertebrate type on all coasts where its dreaded enemy is 

 found ; but on the Atlantic shores of England and France, or the 

 high northern coast of America, or the west coast of N. and S. 

 America, and the Galapagos Islands, there is no Periophihal- 

 mus, and Ofichidmm has neither dorsal eyes nor dorsal glands. 

 Whether it is worth while to develop ninety-eight eyes on one's 

 back in order to be ready to shoot perpetually at a terrible enemy 

 is an open question. It would seem more peaceful and easy to 

 be swallowed up at once than to live in such a perpetual state of 

 apprehension. 



1 think all the instances I have given will show in what an 

 extraordinarily interesting way the environment of an animal will 

 act upon its visual organs. Gradually, in the course of ages, the 

 highest animals of all the higher divisions of the animal kingdom 

 have found the head the most useful position for eyes for all pur- 

 poses. But Nature was quite prepared to develop eyes upon any 

 part of the body, and has by no means forgotten how to do so 

 still. The star-fish has an eye-spot at the end of each arm, as 

 though a dog had an eye at the end of each paw. In the Chito- 

 nidce (Gastropod Molluscs) Thoresby has detected more than 

 10,000 eyes on the exposed surfaces of their shells. The scallop 

 has eyes placed all along its mantle. An annelid, Polyophthalmus^ 

 has a pair of eyes on every segment of its body, and some worms 

 have eyes on the last segment of their bodies. Some have eyes 

 on their tentacles, and others on their gills. 



People are sometimes fond of constructing romances, where in 

 imagination they visit other planets. The people in these planets 

 always turn out to be distressingly like ourselves. It appears to 

 me that if planets were described as inhabited by invertebrate 

 animals grown big and intelligent, we should have very novel and 

 amusing conditions of society to describe. A planet inhabited 

 permanently by a set of old maids, where gentlemen were grudged 

 even a few days of life, and one matron presided over the whole 

 community, where also there were no paupers and no starvation, 

 and children were brought up as in the Republic of Plato, would 



