94 EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



frequently into the side-gutters than any other one place. Only a sugges- 

 tion of segregation is seen in 5 and 6 in Epilachna borealis. Here we see a 

 variation curve strongly skew in the direction of confluence of spots, and 

 the experiments in heredity give us progeny which seem for the most part 

 intermediate, but nearly always there are many without confluence and 

 some with fully as much or more than the parent. Here, then, confluence 

 is not swamped, because, in spite of the majority of intermediate and 

 normal progeny, a mechanism, in some ways suggestive of that which 

 produces de Vries's ever-sporting varieties, maintains the supply of these 

 confluent individuals. 



In Coccinella novemnotata we have a type of heredity that deserves fur- 

 ther mention. Here the variation consists of a series of steps. We have 

 4 spots in which we may have no confluence, or confluence of 2, of 3, or of 

 4 spots. Intergrades exist in which there is an approach to confluence or 

 partial confluence; nevertheless the steps referred to constitute centers of 

 variation more frequented than intermediate conditions. Now, the progeny 

 may belong to the centers of variation of their parents, but also to the 

 other centers. The variation is, then, moniliform and the heredity poly- 

 morphic. 



The facts of variation and distribution in these genera show us that the 

 swamping influence of intercrossing is not effective upon a large number 

 of varieties. This immunity is obtained by some degree of segregate 

 heredity. Absolute segregate heredity is not found, hence we may con- 

 clude that a variety may be protected from swamping by an only partly 

 segregate heredity. 



PHYLOGENY. 



It is desirable if possible to decide upon the primitive pattern from 

 which the coccinellid beetles were descended. Schoeder, while admitting 

 that the pattern of Adalia bipunctata and its varieties are referable to a 

 scheme of 7 spots and a scutellar mark, contends that the primitive pattern 

 was one of vittae. This was followed by barring, and a reduction of the 

 network thus formed left the points of intersection as spots. 



That the primitive pattern was one of vittae may be possible if we go 

 back to a sufficiently remote time. It is possible that coccinellids having 

 as regular vittae as those of Paranaemia vittigera have retained this pat- 

 tern, with possibly some reduction in the number of vittae. Tower (1906) 

 finds that vittae in Leptinotarsa are between the veins, yet the extension 

 of pigment along the veins in modification experiments in the lady-beetles 

 makes it possible that the vittae were here differently placed. In Adalia 

 these spots are upon the veins, but this can not be said to be the general 

 rule. The position of the spots seems to be remarkably independent of the 

 veins. The influence of the vein is much more evident in projections from 

 the spots along the linea externa in Coccinella novemnotata and Harmonia 

 picta. 



