MOVEMENTS IX THE VISUAL CELLS 123 



Movements of the inner member of the vertebrate cone cell 

 were first observed by Stort in 1884, although the earliest an- 

 nouncement of this discovery was pubhshed by Englemann 

 ('85) in whose laboratory Stort worked. To the contractile 

 portion of the cone's inner member Englemann applied the sig- 

 nificant term 'myoid' (figs. 30, 31; my. con.). The contractility 

 of the myoid is extraordinary, since in some fishes light produces 

 a shortening of this part to 10 per cent of the length which it 

 assumes in darkness (figs. 25, 27). If effective at all, fight 

 always causes a shortening and darkness an elongation of the 

 cone cell. 



Stort ('87) extended his first discovery on the frog by experi- 

 mentation upon representatives of the various other vertebrate 

 classes, thereby showing that in fishes and birds extensive move- 

 ments of the cones likewise occur. In the salamander, as a type 

 of urodele amphibian, responses of the cones to fight have both 

 been asserted (Angelucci, '90), and denied (Garten, '07). Among 

 a few reptiles (Englemann, '85) and mammals (Garten, '07) 

 slight changes have apparently been detected. 



The visible response of the rod's inner member presumably 

 is not identical throughout all the vertebrate classes. Angelucci 

 ('84) was the first to observe a shortening of the frog's rod after 

 exposure to light and later, in 1890, he applied the term 'myoid' 

 to the contractile portion of the rod's inner member (figs. 30, 

 31 ; my. bac.) in a sense similar to that in which Englemann has 

 previously used it for the corresponding jiortion of the cone; 

 Arcoleo ('90) likewise reported that the rod myoid of the toad 

 shortens in the fight. Recently, however, Lederer ('08) has 

 asserted that the photomechanical change in the rod myoid 

 of the frog is not a shortening but an elongation. In all fishes 

 that possess cones, the rod myoid lengthens in the fight and 

 shortens in darkness, as Stort ('87) first believed. The response 

 in the rods of day-birds (Stort, '86) is similar to that in fishes, 

 although in night-birds (Garten, '07) movements of these cells 

 may be entirely absent. No experimentation has been per- 

 formed upon the rod cells of mammals or of reptiles ; in the latter 

 group, however, the retina usually lacks these elements. 



