30 S. J. HOLMES 



placed on a glass plate on a tripod and illuminated from below. 

 When my hand was passed beneath the jar, thus throwing a 

 shadow on the larvae from below, they would swim downward 

 as before. Momentarily turning off the light produced the 

 same effect. An object placed on a fine wire and brought near 

 the wriggler from below when it was hanging from the surface 

 film would invariably cause a sudden descent towards the ap- 

 proaching object. When larvae are on the bottom, shadows 

 thrown upon them either from above or below simply set them 

 into commotion, which does not issue in any very definitely 

 directed movements. 



Notwithstanding this peculiar reaction to shadows and the 

 direction of the light rays the larvae of Culex often show a 

 markedly positive photo taxis. Frequently I have seen them 

 gathered on the side of their jar toward the window and when 

 brought into a dark room and exposed to an incandescent, 

 sixteen-candle power electric lamp they swim over toward the 

 more illuminated side of the dish. Larvae vary greatly in their 

 phototactic response. Many seem entirely indifferent to the 

 light. Certain individuals swim toward it eagerly and will 

 follow it about when it is passed from one side of the dish to the 

 other, with great promptness. One lot of larvae three days old 

 was strongly positive, the whole troop swimming over to what- 

 ever side of the dish the light was held. The same larvae, how- 

 ever, when suddenly struck by a shadow will go away from the 

 light rays with equal readiness. Mosquito larvae are very sensi- 

 tive to jars. Tapping lightly on their vessel sends them quickly 

 downward. Placed before a window or illuminated from one 

 side by an artificial light they swim downw^ard and away from 

 the light whenever they are jarred just as they do when dis- 

 turbed by a shadow. 



There is no orientation in the light response. This is in fact 

 practically impossible owing to the peculiar method of swimming 

 which consists in bending the body rapidly from one side to the 

 other. The larvae swim sidewise or obliquely to the direction 

 of the rays when they go toward the light, as they do in swim- 

 ming away from it. When they have arrived at the positive 

 side of the dish the position of the body bears no relation to the 

 direction of the rays of light. The lack of orientation in the 

 larvae may not be of significance in regard to the nature of the 



