22() LESLIE B. AREY 



and antorior rectus and the ventral oblique muscles (those inner- 

 vated by the oculomotor nerve) were cut, leaving the eyeball 

 attached to the body by the two remaining muscles. Under 

 these conditions, the pigment migrated much as in a normal 

 animal. 



Hence it appears that the inhibitory mechanism has been 

 located as existing in association with the muscles (or possibly 

 the blood vessels of the muscles) which are innervated by the 

 oculomotor nerve. The objection may be raised, however, that 

 there is a possibility of the dorsal oblique and posterior rectus 

 muscles possessing an inhibitory function also, but that the inhibi- 

 tion produced when only two muscles are left in connection with 

 the eye is not sufficient to prevent the pigment response. The 

 evident check experiment which answers this criticism consists 

 in severing all the muscles except two which are innervated by 

 the oculomotor nerve. When this was done (the dorsal rectus 

 and the inferior oblique being left intact) no movement of the 

 pigment was observed. This result indicates that the inhibi- 

 tory mechanism is found associated with those muscles inner- 

 vated by the oculomotor nerve and is not demonstrably asso- 

 ciated with the other eye muscles. 



Since the dorsal oblique and posterior rectus muscles are not 

 potent in restraining pigment migration, it was possible to make 

 the following experiment. All the muscles excepting these two 

 were cut and light-adapted fish with the optic nerves either intact 

 or severed were placed in a dark situation. If the retinal pig- 

 ment contracted under these conditions, it could be reasonably 

 assumed that the presence of a partial vascular circulation had 

 been responsible for the change. However, no movement of the 

 pigment was detected, yet as the blood vessels in these muscles 

 are small in number and size, the results neither support nor 

 detract from the general view that absence of blood supply pre- 

 vents pigment contraction in the dark. 



Although the relation of the autonomic fibers to the oculo- 

 motor nerve of teleosts has not been worked out as completely 

 as in some other forms, it is at least evident that from the ciliary 

 ganglion the so-called ciliary nerves pass to the eyeball, probably 



