Il8 Isabel McCracken. 



outdoor conditions is unknown, but under laboratory conditions 

 at least five generations may be secured. 



The object of the present experiment was to observe through 

 several generations the behavior of the particular differentiating 

 character, color, with the view of testing for this insect Mendel's 

 principles of dominance and segregation. 



The particular circumstances that make Lina lapponica favor- 

 able material for this study are these: 



1. Both sexes are dichromatic. 



2. The sexes are easily distinguished on account of the differ- 

 ence in size. 



3. Individuals may be mated for life, or males of one brood 

 may be allowed to mate freely with females of another, thus secur- 

 ing diversity of partners (the plan without doubt pursued in 

 nature), while securing the same lineal record for the offspring. 



4. Life habits are adapted to laboratory conditions. 



5. At least five (probably more) generations may be reared in 

 a single season. 



This work was not begun until the first generation of Lina for 

 the present year had come to maturity. However, the four 

 succeeding generations studied offer some interesting and instruc- 

 tive data that will be supplemented another year when an earlier 

 brood will be secured. 



II. CHARACTER OF THE MATERIAL USED IN THE EXPERIMENTS. 



For the initial study, about 1000 individuals in the last larval 

 stage were collected from willows between April 20 and May 4, 

 1904. From these a total of 600 adults were secured, the rest 

 having fallen prey to a parasitic fly. This lot contained a repre- 

 sentative number of males and females, and the dichromatic 

 extremes of color. 



Individuals in one of the two color and pattern series have, as 

 previously stated, wing covers with ground work of brown, dotted 

 with fourteen black spots (PI. I, Fig. 4). There is considerable 

 variation in shape, size and coalescence of spots, but no apparent 

 variation in ground color. Individuals representing this color 

 type are referred to in this paper as S. In the other series the 

 individuals are wholly melanic or black (PI. I, Fig. 6). These 

 are here referred to as B. In each series the thorax is similar. 



