NO. 10 



TROPISMS OF LEPIDOPTERA — McINDOO 



47 



Vom Rath (78) first described a flask-shaped structure in the distal 

 segment of the labial palpus of the cabbage butterfly. The structure 

 is lined with innervated hairs which he considered olfactory in func- 

 tion. He imagined this structure to be a special olfactory organ for 

 detecting the presence of food. This structure, whose shape varies 

 considerably, seems to be common to all Lepidoptera. It was seen in 

 practically all of the specimens examined by the present writer. It is 

 present in the labial palpi (fig. 5, E, Bo) of both sexes of the codling 

 moth, in which it is sac-shaped, opening to the exterior by a wide mouth 

 (fig. 15, A). The innervated hairs (fig. 15, B, Hr), instead of being 

 narrow and hollow as figured by vom Rath, are wide, heavy, and club- 



FiG. 15. — Sense organ in labial palpus of codling moth. It is probably a static 

 or balancing receptor. A, Diagram of a longitudinal section through terminal 

 segment, showing organ made up of sense hairs (Hr), sense cells (Sc), and a 

 large nerve (A'') ; B, drawing from an oblique section, showing same parts, 

 X750. 



shaped. They certainly cannot be olfactory in function. Since their 

 slender bases arise from very delicate chitin, their clubbed ends prob- 

 ably swing in various directions as the insect moves about. This organ 

 reminds the writer of the statocysts, especially those of the shrimp and 

 crayfish, and it probably has a similar function. If it does not contain 

 statoliths, the hairs may operate sufficiently without the use of them. 



VI. OTHER RECEPTORS 

 Among the general sensations of Lepidoptera might be mentioned 

 those of temperature, humidity, direction, hunger, fear, and pain, but 

 they are probably not connected with special sense receptors. 



