THE DISTRIBUTION OF VARIANTS IN NATURE 103 



(g) Humble-bees. — Many species of humble-bees, besides 

 geographical variation, show marked polymorphism in parts 

 of their range. Certain species, such as Bombus solstitialis 

 and B. soroensis, which arc extremely variable in Central 

 Europe, are almost constant in England. 



(h) The Coccinellid beetle, Harmonia axyridis. — Dobrzansky 

 (1924) shows that this species varies in colour from yellow to 

 black, the colour-pattern of the elytra falling into eight main 

 classes. Most of the variations can be found all over the 

 range in different proportions, with the exception that in the 

 western part of its range (Russia to Japan) there is a tendency 

 for a single form, H. axyridis (typical), to dominate the 

 others. 



(i) The previous type of variation may be compared with 

 instances of local specific intergradation, which give rise 

 to a similar distribution of variants. Thus von Schwep- 

 penburg (1924) notes that the sparrows Passer domesticus and 

 P. hispaniolensis, in various subspecific forms, inhabit most of 

 Europe, N. Africa and Asia without interbreeding, but in 

 large areas of Algeria, Tunisia and in Malta they interbreed 

 so much that it is hardly possible to find specimens true to 

 either type. 



Barrett-Hamilton and Hinton (191 5, pp. 545~6) record 

 that the mice Apodemus jlavicollis and A. sylvaticus, which 

 occur more or less commonly together in England, occupy 

 different habitats in Norway. In the latter country the 

 lowland mice of the south are nearly all sylvaticus, while those 

 of the high upland pastures are jlavicollis ; in intervening 

 areas intermediate forms occur, almost certainly as a result 

 of cross-breeding. 



(j) Fernald (1906) shows that the American sand-wasp 

 Chlorion cyaneum and its race C. c. aerarium differ in average 

 size and in colour. The typical form is mainly southern and 

 aerarium mainly northern, but they overlap over a wide area 

 and occasional specimens of aerarium are found very far south. 

 He records the same type of variation in C. thomae (with var. 

 bifoveolatum) , and Porter (1926) found a similar relation in 

 Sceliphron cementarium between the forms servillei (southern) 

 and Jlavipes (northern). In other species of Chlorion Fernald 

 found more complicated variation. Thus in C. ichneumoneum 

 there are three forms, one found in U.S.A. between Maine and 



