28o OUR HOUSEHOLD INSECTS 



the Diptera, through the suppression of parts which are, 

 except in this order, almost universally present, and 

 generally very prominent. This suppression and simpli- 

 fication is the more remarkable because the bugs are in 

 some respects a more primitive race of insects than the 

 flies, and might so far have been expected to show a 

 more generalised type of mouth. It is impossible at 

 present to do more than speculate as to the significance 

 of this absence, as separate organs, of parts which are in 

 most insects amongst the most prominent of the food- 

 taking apparatus, and which are endowed with such a 

 power of persistence, so to speak, that in some cases 

 they remain distinct after the organs to which they 

 belong, and of which they are appendages, have become 

 fused with the rest, or have disappeared altogether. 

 Too little is yet known of the function or functions of 

 palpi in general, to be able to imagine what can be the 

 influence upon the economy of the insects of the defect 

 under which they labour. One would think that by 

 contrasting the habits of the not -palpi -possessing 

 Hemiptera with those of the palpi-possessing Diptera, 

 it would become possible, by detecting constant differ- 

 ences between the two orders, to arrive at some valid 

 conclusion as to the function of these organs. Such, 

 however, does not seem to be the case ; and if there is 

 any marked difference in the way of taking the food, or 

 in other respects, it has yet to be discovered. We know 

 no more why the blood-sucking mosquito should possess 

 palpi than why the equally blood-sucking bug should be 

 without them. Some maintain, however, that the 

 channel-like beak itself consists of the fused labial palpi 

 instead of the pair of jaws to which they belong, in 

 which case the above remarks would lose some of their 

 force. 



