590 



BRADLEY M. PATTEN 



TABLE 2 



A table showing the deflections of the 15 larvae kept isolated throughout the experi- 

 ments. The measurements given represent the average deflection of a "right and 

 left pair of trails" such as that shown in figure 2, c. R indicates that it was not 

 possible to make the larva move at all. This rarely happens except immediately 

 before pupation. * indicates the replacement of a dead larva by a fresh indi- 

 vidual of the same age. P indicates the pupation of the larva, p, number 12 

 pupated the following day. 



By computing the average deflection of the 100 trails made 

 daily by the 50 larvae, the sensitiveness of the culture as a whole 

 could be accurately determined. These measurements were 

 plotted graphically in the form of an age-sensitiveness curve. 

 The curve thus obtained is shown in figure 3. Deflection in de- 

 grees is plotted along the vertical axis, and age in days along the 

 horizontal axis. 



It is interesting to compare with this smooth curve compiled 

 from the average reactions of the culture as a whole, a series of 



Fig. 2 Photograph of trails showing the characteristic reactions of larvae at 

 various ages. Each pair of trails represents the reactions of a larva to changes of 

 90° in the direction of incident light made first on its right side (lower trail of 

 pair) and then on its left side (upper trail of pair). The sharpness with which 

 orientation to the new light direction is accomplished is regarded as an index of 

 the degree of photosensitivity. 



