is very ancient and is represented in Baltic amber. How- 
ever, in appraising the value of the evidence supplied by 
fossils with regard to the antiquity of particular genera 
and species, we have to urge caution regarding the signi- 
ficance of negative evidence because fossils in museum 
collections constitute a pitifully incomplete record of the 
past. 
From the known examples of orchid-insect symbiosis 
it becomes clear that orchids have derived profit from two 
of the dynamic urges of animals: hunger and sea. In 
Coryanthes and Catasetum the pollinating insects seek 
food. The flowers of these genera have developed edible 
tissues that attract certain bees, and in the course of evo- 
lution their floral structures have become so modified 
that food-seeking bees bring about pollination. In Oph- 
rys, on the other hand, where nectar is wanting, and in 
several of the better understood members of this genus 
which seem to lack edible tissues, it is not the urge of 
hunger that motivates the insects necessary to effect pol- 
lination, but the equally dominant sex-impulse. Probably 
in the course of evolution, these orchids gradually lost 
the capacity to produce nectar or edible tissues and by 
some passive response to stimuli incident to the dynamic 
sexual urge of certain insect-visitors became so modified 
in structure that they seem to simulate the female of a 
particular insect species. In this connection it is difficult 
to escape the conclusion that such orchids as Ophrys 
speculum, by “‘mimicking’’ the female, in becoming by 
evolution dependent for pollination on the male of a sin- 
gle species of insect, have been marvellously even if peril- 
ously specialized.’ In the final analysis there is something 
"Ophrys speculum is a widely distributed species in the Mediterranean 
region and it is not at all improbable but that as its pollination history 
becomes better known we may find other insects associated with the 
transportation of the pollinia. 
[16 ] 
