HONEY-DEW 165 



in fertilisation and tlie subsoqucnt outprrowth of fruit and 

 seeds. Tims a year's cycle of the plant-lice exactly answers 

 to the life-history of an ordinary annual. Thecf?f,'s corre- 

 spond to the seeds ; the various generations of aphides 

 budding out from one another by parthenogenesis corre- 

 spond to the leaves budded out by one another throughout 

 the summer ; and the final brood of perfect males and 

 females answers to the flower with its stamen and pistils, 

 producing the seeds, as they produce the eggs, for setting 

 up afresh the next year's cycle. 



This consideration, I fancy, suggests to us the most 

 probable explanation of the honey-tubes and honey-dew. 

 Creatures that eat so much and reproduce so fast as the 

 aphides are rapidly sucking up juices all the time from the 

 plant on which they fasten, and converting most of the 

 nutriment so absorbed into material for fresh generations. 

 That is how they swarm so fast over all our shrubs and 

 flowers. But if there is any one kind of mat.^rial in their 

 food in excess of their needs, they would nati rally have to 

 secrete it by a special organ developed or enlaiged for the 

 purpose. I don't mean that the organ would or could be 

 developed all at once, by a sudden effort, but that as the 

 habit of fixing themselves upon plants and sucking their 

 juices grew from generation to generation with these 

 descendants of originally winged insects, an organ for 

 permitting the waste product to exude must necessarily have 

 grown side by side with it. Sugar seems to liav'3 been such 

 a waste product, contained in the juices of the plant to 

 an extent beyond what the aphides could assimilate or use 

 up in the production of new broods ; and this sugar is there- 

 fore secreted by special organs, the honey-tubes. One can 

 readily imagine that it may at first have escaped in small 

 quantities, and that two pores on their last segment but 

 two may have been gradually specialised into regular 



