36 _ THE FERTILISATION OF FLOWERS. [PART II. 
developed to insure greater success in the search after food ;* and 
we can distinguish how a dependence on flowers has sprung up at 
different epochs of time, for in some beetles there has been time 
for the attainment of adaptations, and then for their divergence 
to form genera and families; while others, which have acquired 
the habit later, remain isolated anthophilous species among near 
allies which never resort to flowers. 
Diptera and Thysanoptera. 
The Diptera stand on a higher grade than the Coleoptera in the 
matter of adaptation to a floral diet, and are of far more importance 
for fertilisation. While only a small fraction out of all the 
species of Coleoptera resort to flowers, probably the majority of the 
Diptera do so. While, further, the mouth-organs of our native 
beetles show only commencing adaptations, which extend at 
most over small families, and may be easily traced by intermediate 
stages to their origin, in flies and gnats the mouth is so deeply 
modified that it is exceedingly difficult to trace back its parts to 
the primitive form of the original biting insect-mouth. For our 
present purpose it will suffice to discuss the structure of the 
mouth-organs and the manner of using them in those Diptera which 
are specially important as fertilisers of our native flowers, without 
entering into questions of phylogeny. 
The family of the Drone-flies, etc. (Syrphide), are alone of far 
more importance as fertilisers than all our other Diptera put 
together. Most of their numerous and often very common specie 
depend mainly or exclusively on a floral diet, and in this family aa 
found the most perfect adaptations to a diet alternately of polle: 
and honey. Accordingly, to illustrate the mouth-organs of flies, 1 
1 T have fully discussed the development of a dependence on flowers in beetles in 
a special work. This treats of the first transition to a floral diet; the progress 
towards entire dependence on honey and pollen; the attainment through practice 
of a certain ease of action upon flowers, and its hereditary transmission; and 
the similar behaviour of different beetles which have acquired equal degrees of structural 
adaptation (H. Miiller, ‘“‘Die Entwickelung der Blwmenthdtigkeit der Insekten,” 
Kosmos, Bd. ix. pp. 258-272). , 
9 
* The above refers only to our indigenous forms. Tropical and subtropical beetles 
show far more striking adaptations to a floral diet. For instance, in a Wemo 
which my brother Fritz Miiller observed sucking flowers of Convolvulus at Itajahy 
and sent to me, the maxilla are transformed into two sharp grooved bristles 12 mm. | 
long, which when opposed form a tube like the proboscis of a butterfly, but of course 
not capable of being rolled up (cf. H. Miiller, “ Hin Kafer mit Schmetterlingsriissel,”’ 
Koemos, Ba. vi. pp. 802-304 ; Hagen, Proc. of the Boston Soe. of Nat. Hist. vol. xx. 
pp. 429, 430, 1880; H. Miiller, Kosmos, Bd: x. p. 56). 
% I have explained my view of the descent of Diptera from Phryganide in a 
paper entitled ‘‘ Anwendung der Darwin’schen Lehre auf Blumen und blumen- 
besuchende Insekten,” Verh. der Naturh. Ver. fiir pr. Rheinl. u. Westf. 1869. 
