THE MANIFESTATION OF THE FLIGHT-FUNCTION 

 IN THE SILKWORM (BOMBYX MORI). 



ISABEL Mccracken. 



The activities of the adult silkworm moth {Bombyx inori) are 

 normally confined to those connected with the reproductive re- 

 flexes, mating and ovipositing.^ The moth issues from its cocoon 

 sexually mature and lives in a perfectly functional condition for 

 several days without taking food and scarcely wandering from its 

 birthplace. Its thoroughly domesticated condition and asso- 

 ciated habits call for the exercise of but few of the usual insect 

 instincts. In particular, searching for food and for mates having 

 been dispensed with, the flight-function is a useless function and 

 rarely manifest. 



In general appearance, the newly emerged moth is a perfectly 

 formed insect. A close inspection, however, shows vestigial 

 mouth-parts, the taking of food having thereby become an im- 

 possibility. Otherwise, the various anatomical features are normal. 

 The wings, particularly, are of perfect form and under perfect 

 control so that the exercise of the flight-function is a possibility, 

 though as stated the insects are rarely observed to fly. 



" The presence of an organ," says Folsom,^ " normally implies 

 ability to use it. The newly born butterfly needs no practice 

 preliminary to flight." The silkworm appears, from general 

 observations, to be an exception to this rule. At any rate the 

 non-flight habit has seemingly become fixed, absolutely so in the 

 case of the female, but in the case of the male with exceptions 

 and under special conditions to be herein noted. 



This non-flight habit is such a common observation among 

 silkworm breeders that investigators have made use of the wing 

 of the silkworm moth to study indications of its structural degen- 



1 Kellogg, "Some Silkworm Moth Reflexes," Biol. Bull., V., pp. 152-154. 

 McCracken, " The Egg-laying Apparatus in the Silkworm as a Reflex Apparatus," 

 Jour, of Comp. Neitr. and Psychol., XVII., pp. 262-285, ^QO?- 



^ Folsom, " Entomology," p. 357. 



