on Flower-Haunting Diptera. 121 



One point which comes out very clearly in many 

 different cases is also illustrated by the buttercups. 

 That is, that the water-loving forms of a genus, such as 

 in this case R. aquatilis and B. sceleratus, are visited by 

 perfectly extraordinary swarms of very low-class Diptera, 

 while the guests of the land-forms though fewer in 

 number, are of a much higher type (^.g., R. ficaria, 

 V.S.). These water species of a genus are also usually 

 botanically less specialised than their land allies,* so that 

 the specialisation of the insects and of their hosts has 

 advanced together. 



This corresponding rise in the scale of specialisation 

 of guests and host together comes out very clearly in a 

 variety of genera, and is strongly in favour of the 

 correctness of the general theory to which I shall allude 

 later on. Thus Geutn urbanum is yellow and of a simple 

 open type, and is visited by Siphona geniculata, 

 Hydrotea dentipes, Anthomyia radicnm, and Hylemyia 

 sirigosa, 



Geuni rivale is red and of a very much more com- 

 plicated type, and this is visited by Bomhns muscorum 

 and hortorntii, as well as RJtingia rostrata. 



Epilohium angustifoliunb has also a larger, more 

 tubular and one-sided flower than the ordinary willow 

 herb E. monfanum. Hence ono finds upon it the hive 

 bee and bumbles as the most regular visitors. {Ajns, 

 Bombu-s Jncorum, B. pratonim, Vespa sylvestris, and 

 Cyrtoneura stabnlariti). 



The other only received the visits of Syritla pipiens, 

 Platychirus clypeatus, tSiphona cristata, and Anthomyut 

 radicum. 



The cloudberry, Rubns duirnxmorus, is also either 

 degraded or an earlier form of Rubus than the common 

 blackberry, and hence it is not surprising that only a 

 species of Empis, which Mr. Brunetti thinks is new to 

 Britain, Anthomyia radicum, Siphona cristata, and 

 Hydrotea dentipes were discovered upon it. Two very 

 curious instances of the effect of structure of flower on 

 insect visitor may be mentioned in this connection. 

 Corydalis, a kind of poppy, belonging to one of the earliest 



i?. sceleratus has small petals, conical axi?, etc., and R. aquatilii 

 is white, not yellow. 



