66 J. FRANK PEARCY AND THEODORE KOPPANYI. 



of the organ for light perception. We avoided injury to the brain 

 and otic capsule and the immediate post-operative behavior of 

 the fish proves that there were no lesions of those organs. 



Any continuous tilting of the fish is called a "forced position" 

 by Loeb. Loeb discriminates in one of his earliest papers between 

 two different types of forced responses: "forced movements and 

 forced position." "Wir sprechen von Zwangsbewegungen, wenn 

 die Tiere sich kontinuirlich oder sehr haufig in Bahnen bewegen, 

 die von denen eines normalen Thieres unter den gleichen Um- 

 standen in einem bestimmten einfachen Sinne abweichen." And 

 on the other hand: "Wir bezeichnen als Zwangslagen die 

 Abweichungen von der normalen Orientierung gegen den Schwer- 

 punkt der Erde." 



According to Loeb the forced positions are due to geotropism. 

 Moreover, he refers to the fishes as one of the clearest instances of 

 such phenomena. The normal position of fishes in swimming or 

 at rest is also, according to Loeb, a geotropic phenomenon. 

 " Versuchen wir es einen solchen Fisch gewaltsam auf den Riicken 

 zu legen, so widerstrebt er und bringt, so bald wir ihn wieder frei 

 lassen, sich wieder in seine gewohnte Orientierung zuriick." 



Even the position of the eyes are influenced by the gravitation 

 in the fish. "Bringen wir den Kopf eines Fisches gewaltsam in 

 eine andere als die ihm zukommende Orientierung gegen die 

 Schwerkraft der Erde, so gehen die Augen vollig oder theilweise 

 in die alte Orientierung zuriick. . . . Das Licht hat mit diesen 

 Erscheinungen nichts zu schaffen, sie treten auch, wie bekannt, 

 im Dunkeln und bei vollig Erblindeten ein." (Loeb 5 ). As Loeb 

 points out the orientation of the fish in relation to gravity takes 

 place by means of the otolith apparatus, as first demonstrated by 

 Mach and Breuer. Loeb cut (in Scyllium caniculd] the right 

 VHIth nerve. He saw forced circus movements to the side of 

 the lesion, forced tilting toward the side of the lesion, pleuro- 

 thotonus, and compensatory positions of the eyeball and fins. 



Bethe does not deny the static function of the labyrinth, but 

 he states that the geotropism of the Elasmobranches is not 

 essentially changed by the removal of one labyrinth. He failed 

 to observe in many animals the forced positions as after-effects of 

 unilateral labyrinth -extirpation, but admits that forced move- 

 ments and forced positions of the eyeballs and fins can often be 



