HIPPODAMIA. 



31 



spots are, therefore, to a considerable degree independently variable units. 

 Yet if we take into consideration the combination of spots, we shall find 

 there is some ' ' coupling. ' ' Spot 1 is most frequently the only spot absent, 

 while spot 3 is most frequently absent as one of three. It is quite possible 

 that the order of disappearance would be just the reverse of the order of 

 persistence. Table 9 and fig. 18 are designed to test this matter and also 

 the question of coupling between spots. Along the horizontal scale I have 

 represented the various combinations of spots in the order of frequency of 

 their disappearance. The solid line indicates the frequency of these sev- 



Spots 



["12116111113112841341541122318. a 

 6 22 34254 5363626 4 523455346 



3 66 66 5 5 45 



Lackin-' 3583664327313241241168157 73 72 41 32 26 25 19 18 14 10 9 8 77 6 5 4 1 1 1 00 06073 

 Having" 0431024101091013390256 13 660418 26 14 6211 



Fie. 18. Correlation of los- of spots. 



eral patterns. Now, in the dotted line I have represented the frequency 

 of the same combination of spots present. We see from it that spot 4 

 alone is less frequently lacking than spot 2 alone, yet spot 2 alone more 

 frequently persists. Similarly, spots 5-6 are less frequently lacking than 

 4-5, yet 4 and 5 each persist more frequently. The couplings of pairs of 

 spots in disappearance in the order of frequency are 1 and 6, 1 and 2, 1 

 and 3. These pairs do not frequently persist alone, and the order of pairs 

 in persistence is 4 and 5, 2 and 3, 3 and 5 ; these pairs are not frequently 

 lacking. The coupling of trios in order of disappearance is 1-2-3, 1-4-6, 

 1-2-6 ; these groups rarely persist alone. Thus it is roughly true that the 

 more persistent groups are less likely to be frequently disappearing groups. 

 If the confluence of elytral spots 4 and 6 represented merely an overflow 

 of pigment, because of increase of size of spots, it should be found in H. 

 quinquesignata or bowditchi, yet it is only rarely met with in cases of 

 enlarged 4 5 in the mountains. It is more frequently found in Califor- 

 nia in regions where the spotless variety is present. 



