2/6 'Journal of Comparative Neurology and Psychology. 



light rays. This orientation is a position with the long axis of the 

 body parallel to the light rays, and with the head turned away from 

 the source of light. (B) The effect of suddenly blocking the light 

 to which the larvae are reacting phototactically is to cause a new 

 body-orientation by which the head is usually brought to face the 

 direction from which the light had previously come. In either 

 of the cases mentioned above the body-orientation is brought 

 about by a single motor reflex or by a longer or shorter series of 

 motor reflexes, some of which are "over-produced" movements. 

 These movements include the following types: 



1. Forward or backward rotations,*^ or somersaults — These were 

 rotations in an arc, of a few degrees, which directly determined 

 a new swimming position with the head raised or lowered, depend- 

 ing upon the direction from which the light or shadow had been 

 introduced. In other cases these rotations took the form of a 

 variable number of complete rotations through 360°, either back- 

 ward or forward, in which the body of the larva formed a constant 

 part of the circumference. 



2. Revolutions on the longitudinal axis of the body or rollings — 

 The revolutions or rollings took place either to the right or left, 

 but usually in such direction that the back of the larva became 

 directed more or less toward the light. They might be through 

 a few degrees, or they might exceed 90°, in which case the larva 

 fell to the bottom. In the case of larvae one of whose eyes 

 had been injured this revolution took place very rapidly, oftne at 

 the rate of one hundred and fifty per minute, and always in a deter- 

 mined direction, the normal eye over, the injured eye under (Had- 



.LEY 1907b). 



3. Swingings of the longitudinal axis of the body — These reac- 

 tions w^ere swingings in such a direction that the head was brought 

 by the shortest path to face the dark, and the tail to point toward 

 the light. 



^Three similar types of movement are described by Bohn (1905, p. 4) as follows: 



1° Mouvement de manege — I'animal decrit un cercle de plus ou moins grand rayon, I'axe du corps, 

 courbe en arc, faisant partie constamment de la circonference; la rotation se fait tantot dans le sens des 

 aiguilles d'une montre, tantot dans le sens inverse. Parf ois, au lieu de decrire un mouvement de manege 

 pur, I'animal decrit des courbes de rayon variable qui constituent une sorte de spirale. 



2° Mouvement de rotation en rayon de roue — I'axe du corps ne devie pas; il est une des parties d'un 

 des rayons du cercle decrit, et non une partie de la circumference du cercle: la tete peut se trouver a 

 la circonference ou au centre. 



3" Mouvement de rotation sur I'axe, ou roulement: I'animal tourne autour d'un axe longitudinal qui 

 traverserait le corps dans sa longeur; la rotation commence par une inclinaison de I'animal d'un cote, 

 et le sens de la rotation se trouve ainsi determine. Le roulement peut s'accompagner d'un mouvement 

 de translation et devient un mouvement en pas de vis. 



