3l8 Journal of Comparative Neurology and Psychology. 



PROTOPHYTA. 



Mast ('07) has produced a well rounded and thorough piece of work upon the 

 photic reactions of Volvox. Although the form is classified as a plant its locomo- 

 tion is of a protozoan type and so is of interest here. The first part of his report 

 gives an analysis of its curious method of locomotion. His apparatus is carefully 

 planned and the methods applied to determining its behavior are various. Equal 

 attention is given to the reactions of segregated individuals and of large numbers 

 taken together. Volvox is found to orient by phototaxis, although through a pecu- 

 liarity of its locomotion its path is at a slight angle with the light. The light response 

 is analyzed into a series of avoiding reactions of the individuals comprising the col- 

 ony. Various factors such as previous condition of illumination, the stage of devel- 

 opment of the individual, etc., are described as modifying the light reaction. 



COELENTERATA. 



Gonionemus is an interesting object of study as a type of the primitive and unique 

 group of the jelly fishes. Yerkes ('02, '03a, '04, '06) contributed a paper upon 

 its light reactions in a series treating of different phases of its nerve physiology. 

 Morse ('06, '07) has also devoted some attention to the subject. 



According to Yerkes ('03a) Gonionemus is decidedly phototactic under cer- 

 tain conditions of illumination. The response to localized stimulus can be readily 

 seen if the individual in a negative condition happens into a band of light of graded 

 intensity such as may occur at the edge of a shadow. The side of the bell toward 

 the light which is most intensely illuminated contracts most strongly and the animal 

 thus turns back into the shadow. The juxtaposition of contracting and stimulated 

 regions results in a localized response reduced very nearly to its simplest terms. 

 Morse has confirmed Yerkes in the occurrence of directive response by observing 

 single medusae in various conditions of illumination. 



A marked photokinetic effect occurs. As LoEB earlier found for Planaria the 

 medusae will collect in a shadow because as soon as their active movements 

 bring them there they come to rest. This method of non-orienting response to 

 intensity of illumination has been termed negative photokinesis. It has been 

 already stated that a graded field at the edge of a shadow may produce a phototactic 

 orientation of stragglers which directs them back into the shadow. Thus non- 

 orienting light response and phototaxis cooperate. 



PLATHELMYNTHES. 



Three investigations have been recently published upon the flatworms by Parker 

 and Burnett, Gamble and Keeble and Walter. 



Parker and Burnett ('go) so planned their experiments upon the negative 

 Planaria as to determine the importance of the eyes in orientation, and to show the 

 relative importance of light as compared with other factors in locomotion. Single 

 animals were placed at the center of the horizontal surface marked with a circular 

 scale and directed toward the zero point. The angle at which they emerged was 

 recorded, as well as the time consumed in the trip. If individuals with eyes 

 were started toward the light it was found that they would, on the average, bend 78 



