ZOOLOGICAI. SOCIF/I'V HULI.K'I'IN 



il l-H-.li 

 ■I'lie t-ycliils arc closed by elec-tri.-al stiTiiiilal inn. 



lish were normal, as were the eyes of lish that 

 were asleep from the effects of ether. When 

 examined out of the water or in the air, the eyes 

 were the same as when the fish were immersed ; 

 but, in a short time, less than a minute, one 

 could not see the interior of their eyes. Good 

 photographs of the eyes could only be obtained 

 wiiile the fish were immersed. The fact that 

 fish are not near-sighted should be emphasized 

 because some writers have stated that fish have 

 their eyes focussed for near objects most of the 

 time. Fish, while able to see, or to focus their 

 eyes correctly lor distant objects, are also able 

 to change their focus and see near objects. 

 Some fish were observed with the aid of the re- 

 tinoscope that had their eyes properly focussed 

 on objects as close as four inches or even less, 



flow DO FisiiKs Change thk I'ocus of Thkih 

 Eyes. 

 Fishes' eyes are adjusted to see near objects 

 by the squeeze or contraction of the two oblique 

 muscles on the outside of their eyeballs. The 

 squeeze of the oblique muscles makes the eye- 

 balls longer, the condition found in near-sight. 

 To see distant objects accurately, these muscles 

 relaxed, which permitted the eyes to resume 

 their normal shape. The following experiment 

 demonstrates that the accommodation or the 

 near focus of fishes' eyes is produced by the 

 action of the oblique muscles and not by the 

 action of the ciliary or any other eye muscle: 



1. In the beginning the eye of a normal fish 

 was examined. 



2. By means of electrical stimulation ap- 

 plied to the eyeball or its neighboriiood, in most 



riKKEK 

 TIr- c>e is open. Note tlie oval pupil. 

 DiiiurriM—TUi- shape of tlie pupil of the eye of the Puller. 



fish their focus was changed from distant to 

 near objects. 



3. One of the muscles of the eye called the 

 superior oblique, was cut, which jiroduced no 

 change in the focus of the eye. 



■I. Electrical stimulation now did not jiro- 

 duce any change in the focus. It did not accom- 

 modate. 



.5. The muscle which had been cut was now 

 re-united with a thread, sewed together, with- 



RED HIND 



Tlie outer skin of the eyeball ha.s been peeled oti' and the e.vo 

 inuseles removed. The eyeball is held only by the optie 

 nerve which appears as a white cord. 



IHiiuram — Red hind, right eye with muscles removed and skin 

 over the front of the eve pccleil otf. Note the shape of 

 111.' cycli.ill. wider from siilc to side than at the optii- axis. 



