6 



ORIGIN OF EYE AND EAR. 



The tissues of the lowest animals have not been shown 

 to contain any special nerve-fibres, but underneath those 



parts of the surface 

 P 



where, either in the 

 mannerindicated above, 

 or in some other, the 

 effects of external stim- 

 uli are heightened by 

 any structural modifi- 

 cations, there would be 

 a tendency to the speci- 



FiE. I.-Section through the eimple eye of a alizatioU of aU excep- 

 yniing Bytiscus larva (after (jrenacber). n, _ L 



Uypoderm; I, lens; o optic nerve; g, p. tioUally SCnsitlVe tisSUS. 

 mutinied hypodermic cells ; r, retma_ -J 



Moreover, such an 

 oigan as that represented in Fig. 4 might serve either 

 as a rudimentary oar or an eye. It might, indeed, be 

 acted on by the waves both of light and of sound. Such 

 organs — as, for instance, in the case of marginal bodies 

 rouud the edge of certain jelly-fishes (Medusae; see 

 Figs. 8 and 5U) — have been regarded bv some naturalists 

 as eyes, and by others as 

 ears. Haeckel suggests * that 

 stmie may be wtirmth-organs. 



Fig. 8 represents one of the 

 marginal sense-organs of a 

 .Medusa (Ontochis), where ^^e 

 have a row of brillianlly re- 

 fractive spherules, which from 

 analogy are considered to serve 

 as otoliths ; but wliich, under other circumstances, 

 might be, and in fact have been by some, regarded 

 a,« the lenses of a simply constructed organ of vision. 



' " Report on Deep Sea Medusa? ," " Challenger Reports," vol. iv. 



Fig 8.— Auditory vesicle nf Onto- 

 chis Rafter Haeclcel). 



