McCracken, Egg-laying Apparatus of Silkworm. 27 1 



Having determined that eggs were oviposited in neither mated 

 nor unmated moths until twelve to twenty-four hours had elapsed 

 after issuing, an effort was made to induce early ovipositing by 

 means of external stimuli. In unmated insects (Series 3) and in 

 mated insects from which the males had been early removed (Se- 

 ries 4) the abdomen was stroked with pencil or linger for a few 

 seconds, or gently pressed, at various times during the period pre- 

 vious to the normal time for ovipositing. (This, and the rubbing 

 of the abdomen by the male, had been previously found to be 

 effective stimuli in inducing ovipositing in decapitated moths.) 

 This stimulation met with no response, but ovipositing beginning 

 at the normal time was continued from one to three days (rarely 

 four) in the mated insect and from seven to ten days in the unmated 

 insect. If it is true that the brain in insects may be looked upon 

 as a reflex-inhibitory center, then, as set forth by Bethe with 

 reference to various movements, here the ovipositor fails to respond 

 to a stimulus that is unfailing in a moth with brain removed, 

 because of this inhibitory influence. 



In normal moths, whether mated or unmated, the rate of ovi- 

 positing is irregular. The following shows the time rate for three 

 unmated moths. 



This in general shows the variation observed in time rates in all 

 moths in which time rate data were taken. (Figures indicate 

 seconds elapsing between each successive egg.) 



A— 10, 5, 7, 5, 6, 4, 5, 9, 7, 6, 6, 5, 6, 6, 1 1, 6, 4, 6, 6. Av., i per 6 sec. 

 B— 7, 10, 10,14,5,2,9, 11,9,43,7,9,9,4,6,9,8,21,8,62,9. Av.,i per II sec. 

 C — 1,8, 47, 7, 18, 8, 71, 84, II, 19, 8, 9, 7, 22, II, 10, 12, 9, 15, 10. Av., I per 

 16 sec. The average for all insects timed was from 9 to 12 sec. 



Unfortunately time rates were not secured from day to day for 

 the same individuals amongst normal moths, as in experimental 

 groups. The irregularity in the rate is due to some extent at 

 least to the manceuvers of the ovipositor in (apparently) seeking a 

 favorable spot to place the egg. The movements of the ovipositor 

 previous to the placing of the egg have the appearance of an inten- 

 tional effort to avoid placing one egg upon another. This move- 

 ment was later studied in dethoraxed moths. 



After having determined the behavior of the egg-laying apparatus 

 in the normal insect, twenty unmated moths and about forty moths 

 that had been previously mated were decapitated for Series 5 and 6. 



